User:Sandbh/sandbox

Drive-by Comments Ajpolino

Just a few things in passing. Can't promise the time to really go through this article, though I applaud your substantial work.

• "Sometimes counted as a nonmetal" (lead image caption) references sources from 1844 and 1897. Is there anything more recent that could support that claim? I'm concerned about conflating "this sometimes happens" with "this used to happen". For example I could write "Syphilis is sometimes treated with mercury salts" with an 1896 source, but the world changed and my sentence would be untrue.

@Ajpolino: Many thanks. The "sometimes counted" box has 1844, 1897, 1976, 1993, and 2006 cites. My intent was to show the "sometimes" status has a recurring history. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• The next line "status as nonmetal or metal unconfirmed" cites six sources. Three are called out as verifying the claim about Cn, Fl, and Og. Are the other three all for At? If so, perhaps two can be cut?

I've adjusted the footnote to make it clear that the first three refer to At. The 2013 cite was the pivotal one, predicting that At would be an fcc metal on relativistic grounds. The two other cites, which can be hard to find in the literature, are there to show that it was earlier expected that At would be a metal. Sandbh (talk) 01:07, 21 April 2024 (UTC)

• I have a similar question as my first regarding "There is no widely-accepted precise definition" referenced to works from 2020, 1957, and 1892. What do the earlier works do for us here?

Those three were included to show that since Mendeleev published his 1st periodic table in 1869, the lack of a widely-accepted precise definition has been an ongoing phenomenon. Sandbh (talk) 01:07, 21 April 2024 (UTC)

• References 2 and 10 appear to be the same and can be merged.

Done. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• "Nonmetals closer to the left or bottom ...this occurs in... phosphorus[32]" Are the four sources necessary to support this statement for phosphorus? Also is there a system for when you include quotes in the reference? You do so for just a few scattered throughout.

P is often thought of as being white P whereas the most stable form is black P. The thought of P having some metallic character seems most peculiar, but there it is. The four sources all bring something different to this perspective. I include quotes with references when I feel this would add value to the citation. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• Ditto iodine in the same list (ref 37). At a glance the quote suggests Steudel 2020 would suffice?

Iodine is another oddity. Who would think that iodine, a halogen, would have some metallic character, yet it does. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• "Redmer, Hensel & Holst, preface" (ref 41) and "Criswell p. 1140" (ref 222) consider adding the year for consistency with your other refs.

Done --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• Typo in ref "Smith DW 1990, Inorganic Substances: APprelude to the Study"

Fixed. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• "The number of compounds formed by nonmetals is vast." cited to two different textbooks. Are both necessary to support this relatively simple statement?

Done. Trimmed the older cite. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• Typo in ref 204 "Baja, Cascella & Borger 2022..." should be Bajaj.

Done. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• "They have significant roles in biology" referenced to "Crawford 1968, p. 540; Benner, Ricardo & Carrigan 2018, pp. 167–168:[quote]" assuming the quote comes from Benner, that seems to plenty cover the cited text. Is Crawford needed?

Crawford is important in that they refer to the other nonmetals (H, C, N, O, P, S) as biogens, which is impressive for the time. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• Bertomeu-Sánchez et al. 2002 - you usually spell out three-author refs, but this one gets an "et al." Any particular reason?

Yes, all three authors have double-barreled surnames. I felt that the resulting cite would be clumsily long. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• "Bertomeu-Sánchez et al. 2002, p. 249" is twice, currently as ref 280 and 281.

Fixed. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• Is "Bodner GM & Pardue HL 1993" used anywhere?

Done. I checked for redundant refs just before FAC submission, and evidently missed this one. Thank you, --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• "Reinhardt at al. 2015" typo for et al. (I assume)

Done. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• "the notably reactive halogen nonmetals—fluorine, chlorine, bromine, iodine" is backed up by 9 references. Are these all necessary to support this claim?

There was some controversy among WP:ELEM members as to whether "halogen nonmetals" was a legitimate term rather than "halogens". This was partly fuelled by uncertainty as to whether At was a nonmetal or a metal. The first three references show contempary use of the term. The rest of the cites show alternative terms for the set F, Cl, Br, I. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• Csele 2016 - page numbers would be nice. Unless it has examples of each nonmetal sprinkled throughout (I didn't look)?

Done. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• Are the two Glinka textbooks the same? Is there an edition number to separate them?

Fixed. One textbook was redundant. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• Graves 2022 - I haven't read his book, but a geneticist's memoir seems an odd source to back up statements on boron and silicon reactivity. Not demanding it be changed, but if you have something from a more established source in the chemistry world, that would be nice.

Graves was referring to the absence of silicon-based life-forms on our planet. The mention of boron was missing its separate cite; now addressed. Thanks for that. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• "Gregerson 2023" (ref 206) is this supposed to point to Gregersen 2008 "Radon"? I didn't check to see which spelling and year are correct.

Yes, 2008. Fixed. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• "the notably reactive halogen nonmetals—fluorine, chlorine, bromine, iodine;" similar to above, this is supported by three sources, then two alternative names with three sources each. Is this necessary?

I addressed this point earlier. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• Just checking that Jones 2010, a book called "Pluto: Sentinel of the Outer Solar System" is indeed what's intended here. Didn't read the book. Just surprised the author has a due opinion on distinguishing nonmetals.

Jones was discussing classification science principles, in general. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• "Lémery 1699, p. 118;" points to a 1714 paper. Not sure which is correct.

Fixed --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• "in his classic[289] and influential[290] textbook" I think classic and influential mean the same thing in this context. I'd just pick one.

I feel that Lavoiser's textbook had so monumental an impact on chemistry that two epithets are deserved. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• In table "List of properties suggested for distinguishing metals from nonmetals" Was Martin JW's 1969 book a serious attempt to distinguish metals and nonmetals? A contemporaneous book review suggests the book was targeted at "sixth formers and undergraduates" rather than a work in conversation with the field. Putting my concern another way, is Martin's entry in that table due coverage?

The title of Martin's book is Elementary Science of Metals. It was a part of the Wykeham Science Series of books. The aim was, "To broaden the outlook of the senior grammar school pupil and to introduce the undergraduate to the present state of science as a university study..." For its time it was quite topical. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• "Arsenic is stable in... semi-noble metal." I think the footnote within a footnote is stretching the bounds of due material. If it can't even be squeezed into a first-level footnote, perhaps it should be trimmed from the article?

The first footnote has one reference to each of the six metalloids. Arsenic merits some closer attention given its susceptibility to react with air. I felt that this would be easier and clearer if it was mentioned in a second-level footnote rather than trying to squeeze it in to the first footnote. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• Is Oderberg's opinion (which I'm sympathetic to) due here? Is he considered an important player in this debate?

There is no ongoing debate as such, there is only a lack of agreement in the literature. Since attempts to distingush between metals and nonmetals deal with classifications science, Oderberg's view is a worthy as any other attempt to shed light onto the question. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• "Oxford English University 1989" Is there a reason for the ref to say this instead of "Oxford University Press" or "Oxford English Dictionary"?

Fixed.

• "Radon shows some cationic behavior" do we need both Pitzer and Stein to support this relatively simple claim?

I felt that the notion of radon, a noble gas, showing some cationic behaviour is so mind boggling that it warrented two cites. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• "Rosenberg 2018, p. 847" I assume refers to the citation "Rosenberg E 2013..." but I'm not sure which year is the typo.

Fixed. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

• Could be my ignorance talking, but footnote [af]: "Exceptionally, a study... tiny amounts of uranium." seems like an undue factoid. Do others comment on the exceptional nature of the finding?

Yes, I felt that the thought of F, the most reactive element in the periodic table, being found in native form is so extraordinary that it warranted a mention. --- Sandbh (talk) 01:07, 21 April 2024 (UTC)

Table

Density (D) and electronegativity (EN) in the periodic table

H

He

Li

Be

B

C

N

O

F

Ne

Na

Mg

Al

Si

P

S

Cl

Ar

K

Ca

Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn

Ga

Ge

As

Se

Br

Kr

Rb

Sr

Y

Zr

Nb

Mo

Tc

Ru

Rh

Pd

Ag

Cd

In

Sn

Sb

Te

I

Xe

Cs

Ba

Lu

Hf

Ta

W

Re

Os

Ir

Pt

Au

Hg

Tl

Pb

Bi

Po

Rn

Ra

La

Ce

Pr

Nd

Pm

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Ac

Th

Pa

U

Np

Pu

Am

Cm

Bk

Cf

Es

EN: < 1.9 ≥ 1.9 (revised Pauling) Density:  < 7 g/cm3  D < 7 and EN ≥ 1.9 for all nonmetallic elements ≥ 7 g/cm3  D ≥ 7 or EN < 1.9 (or both) for all metals

Props table2

List of properties suggested
for distinguishing metals from nonmetals

---

Year	Property	Type	Cite
1803	Density and electrical conductivity	P
1821	Opacity	P
1911	Cation formation	C
1927	Goldhammer-Herzfeld   metallization criterion	P
1949	Bulk coordination number	P
1956	Minimum excitation potential	C
1956	Acid-base nature of oxides	C
1957	Electron configuration	A
1962	Sonorousness	P
1966	Physical state	P
1973	Critical temperature	P
1977	Sulfate formation	C
1977	Oxide solubility in acids	C
1979	3D electrical conductivity	P
1986	Enthalpy of vaporization	P
1991	Liquid range	P
1999	Temperature coefficient   of resistivity	P
1999	Element structure (in bulk)	P
2000	Configuration energy	C
2001	Packing efficiency	P
2010	Electrical conductivity   at absolute zero	P
2010	Electron band structure	A
2017	Thermal conductivity	P
2017	Atomic conductance	A
Key: P physical property; C chemical; A atomic

Props table

Chronological list of properties suggested
for distinguishing metals from nonmetals

---

1803 Density and electrical             conductivity 1821 Opacity 1911 Cation formation 1927 Goldhammer-Herzfeld             metallization criterion 1949 Bulk coordination number 1956 Minimum excitation potential 1956 Acid-base nature of oxides 1957 Electron configuration 1962 Sonorousness 1966 Physical state 1973 Critical temperature 1977 Sulfate formation	1977 Oxide solubility in acids 1979 3D electrical conductivity 1986 Enthalpy of vaporization 1991 Liquid range 1999 Temperature coefficient             of resistivity 1999 Element structure (in bulk) 2000 Configuration energy 2001 Packing efficiency 2010 Electrical conductivity             at absolute zero 2010 Electron band structure  2017 Thermal conductivity 2017 Atomic conductance
Key: Properties are physical except for chemical and atomic

Boxes

		Electronegativity
		< 1.9	≥ 1.9
Density (gm/cm3)	< 7
	> 7

Sources

Legend	Source	Elements
	mineral ores	boron (from borate minerals); carbon (coal, diamond, graphite); fluorine (fluorite);[n 31] silicon (silica); phosphorus (phosphates); antimony (stibnite, tetrahedrite); and iodine (in sodium iodate and sodium iodide).
	mining byproducts	germanium (from zinc ores); arsenic (copper and lead ores); selenium and tellurium (copper ores); and radon (uranium-bearing ores)
	liquid air	nitrogen, oxygen, neon, argon, krypton, and xenon
	natural gas	hydrogen (from methane); helium; and sulfur (hydrogen sulfide)
	seawater brine	chlorine, bromine, and iodine

Nonmetal

The term "nonmetal" was unfortunate, since explaining what something isn't is quite hard. From when the article was last at FAC, in October 2023, it's undergone considerable refinement including with respect to prose, the definition, history, tables and images. Much of this work was discussed at the nonmetal talk page, onwards from the section "Outstanding items from FAC7 nomination".

Nonmetal pre-FAC check

Graham Beards, Mike Turnbull, Mirokado, JJE, YBG, Double sharp

Since this article was last at FAC in Oct 2023, I’ve been fine tuning it with the help of the latter two editors.

Much of this work has been discussed at the nonmetal talk page, onwards from the section "Outstanding items from FAC7 nomination".

Aspects of the article worked on have included prose, the definition, history, tables and images.

On a no obligation basis could you please now let me know if you have any concerns about the article before I list it at FAC?

DS @ PT

Re: Firstly, by Lu the 4f electrons are in the core. Yb is the last element where 4f electrons are actually being added, both in the sense of gas-phase configurations (it's already f14s2), and in the sense of chemical activity (it's the last element that can actually use 4f for bonding in compounds like YbO).

From a chemistry perspective, it is the trivalent cations that are important. Here, the configurations are:

f1 f2 f3  f4  f5  f6  f7 
Ce Pr Nd  Pm  Sm  Eu  Gd 

f8 f9 f10 f11 f12 f13 f14
Tb Dy Ho  Er  Tm  Yb  Lu

More specifically, the filling of the 4f sub-orbital is the raison d’etre of the Ln metals (Ce to Lu). While 4f electrons rarely participate in bonding interactions they contribute to the Ln contraction starting in Ce and culminating in Lu, and the uniform and characteristic +3 oxidation state among the metals concerned (Mingos 1998, p. 375; Cotton 2006, p. 12).

Re: But it is still obvious (and was already obvious to classic rare-earth chemists) that Y and Lu are in one bin, and La is in another one.

Well, no. In terms of chemical separation behaviour, that Sc, Y and Lu occurred in the so-called "Y" group, and that La occurred in the “Ce” group did not imply anything particularly significant; it is simply a reflection of the increasing basicity of these elements as atomic radius increases. Taking the alkaline earth metals as another example, Mg (less basic) belongs in the “soluble group” and Ca, Sr and Ba (more basic) occur in the “ammonium carbonate group”. Moving Lu under Y because they occur in the same chemical separation group fails to consider separation group patterns elsewhere in the periodic table.

Further, the separation group behaviour of Y can be ambiguous, and Sc, Y, and La appear to show complexation behaviour different to that of Lu. As observed by Vickery (1960, p. 37):

"In separating Y from the heavy Ln, advantage is always taken of the phenomenon by which Y sometimes assumes characteristics similar to those of the light Ln, and sometimes follows the heavy Ln in behaviour."

Over a decade later Vickery (1973, p. 344) observed that:

"Polymerization of the Y ion has been shown now to account for its apparently nomadic behaviour in earlier classical separation techniques. Evidence is also available for the existence of La hydroxy-polymers in solution. There is, indeed, to be seen an interesting sequence through…Group III in this respect. Hydroxyl bridged polymerization has been shown for Al, Sc, Y, and La ions, but does not appear to exist with the series Ce³⁺ → Lu³⁺. On the other hand, Ga, In and Tl do appear to complex in this fashion. On a thermodynamic basis, ionic hydration—or hydroxo complex formation—may depend upon free energy rather than enthalpy and plots of such free energy link the pre-lanthanon triad more closely to Al, on the one hand, and Ge, etc., on the other, than to the Ln group of elements.

The chemists who kept La under Y were on the mark, chemically speaking.

Re: Why, Lu was even found in Y indirectly: Lu was found as an impurity in Yb, which was found as an impurity in Er, which was found in an impurity of Y. La wasn't found that way; it was found as an impurity in Ce instead.

In fact Y is unique among the rare earth elements in that, depending on the circumstances, it can behave like a light Ln e.g. Pr, Nd, Sm, or a heavy Ln e.g. Dy, Tm, Lu (Marsh 1947, p. 1084; Jowsey et al. 1958, p. 64; Bünzli and McGill 2011, pp. 19, 26; Gupta and Krishnamurthy 2005, p. 165). In terms of the stoichiometry of binary compounds, Y is reported to be more like La than Lu (Restrepo (2018, pp. 94–95). In a similar vein, La has a sufficiently distinct nature compared to the Ce to Lu series (Liu et al. 2019).

Re: There is no relevance of gas-phase configurations, other than as an approximation where one understands not to worry about the little blips at too small a scale for chemistry.

In fact, no less than Scerri argued for the use of gas phase configurations on the basis of the dominant differentiating electron in each periodic table block:

“…for the purpose of selecting an optimal periodic table we prefer to consider block membership as a global property in which we focus on the predominant differentiating electron.” (Scerri and Parsons 2018, p. 151).

It is a simple enough exercise to show that with La under Y there are a total of 12 differentiating electron discrepancies whereas with Lu under Y there are 13.

Re: And the solid-state argument doesn't even support Sc-Y-La because lanthanum metal itself has some 4f contribution, which explains its low melting point.

For Lu, Ratto, Coqblin and d'Agliano (1969, pp. 498, 509) suggested that its lack of superconductivity might be attributable to a small 4f character.

A few other authors referred to some of the properties of Lu being influenced by the presence of its filled 4f shell: Langley 1981; Tibbetts and Harmon 1982; Clavaguéra, Dognon and Pyykkö 2006; Xu et al. 2013; Ji et al. 2015. The most surprising of these is likely to have been Clavaguéra and colleagues, who reported a pronounced 4f hybridisation in LuF₃ on the basis of three different relativistic calculations. Their findings were questioned by Roos et al. (2008) and Ramakrishnan, Matveev and Rösch (2009). More recently Ji et al. (2015) found errors in bond lengths and energies if the presence of a full 4f shell was not taken into account.

An analogous situation certainly occurs at the end of the d-block, in group 12. Zinc and cadmium have HCP crystal structures with c/a ratios of 1.856 and 1.886, much higher than the ideal value (of 1.633). These deviations have been attributed to covalent bonding contributions arising from hybridisation of the filled d band with the conduction band (Steurer & Dshemuchadse 2016, p. 207). Condensed mercury has a distorted structure, and mixed metallic-covalent bonding (Steurer & Dshemuchadse 2016, p. 207; Russell & Lee 2005, p. 354).

In terms of condensed phase configurations, La represents the first occurrence of a 5d electron and Lu the thirteenth. There is no prima facie case for skipping La in favour of Lu.

In a lanthanum table, the number of f-electrons, for the elements in their condensed states, is congruent with the place of each f-block element in 12 of 14 cases; in a Lu table the situation is reversed, with congruency seen in only 2 of 14 places.

Another way of putting it, is that in terms of condensed phase configurations, and in an La table, the 4f row starts regularly wheres the 5f row starts with one irregulary. OTOH, in an Lu table the 4f row starts with six irregularities and the 5f row starts with ten irregularities,

Re: There is simply no counterargument to the stark fact that La has chemical activity of f-orbitals and Lu does not.

The counterargument is that 4f electrons rarely participate in bonding interactions and that the more important consideration is the 4f-induced Ln contraction starting in Ce³⁺ and peaking in Lu³⁺. Further, "...its 4f character, if there is one, is in any case very small (B. Coqblin 1977, The Electronic Structure of Rare-earth Metals and Alloys, Academic Press, p. v).

Re: That is why Landau and Lifshitz are the first writing on the wall, even if they are at least incomplete: they realised that Lu cannot be an f-element. That already makes the Sc-Y-La form illegitimate, because it puts Lu there.

In fact, L&L did not put the writing on the wall, given they placed La above Lu. See, specifically, L&L's depiction of the "Platinum group", as they labelled it.

Re: Talking about covalent vs ionic and all other irrelevancies cannot get around the fact that that is not and has never been what placement in the periodic table is about.

In fact, it was Scerri who wrote that: "Chemically similar groups should be close together, either as vertical groups or horizontal triads, with links between related elements clearly visible." (Scerri 2004, p. 138) Now, it is well known that group 3 are more like groups 1 and 2 than group 4. It then follows that in the 32-column table, group 3 should be adjacent to group 2 rather than group 4. This can only be achieved with group 3 as Sc-Y-La.

Re: ...what placement in the periodic table is about. First it was about valence (Mendeleev 8-column table), and then it became about electronics (Werner's long-form table), in keeping with two of the three chemical revolutions.

It was not fundamentally about valence. Instead it was about the periodic law, expressed by Mendeleev as:

"The measurable chemical and physical properties of the elements and their compounds are…[an approximate] periodic function of the atomic weight [now Z] of the elements."

Valence was used by Mendeleev as an initial sorting rubric. Werner's long form appeared before the structure of the atom was known, before the importance of atomic number was recognised and before quantum mechanics had been developed.

As far as the periodic law is concerned, the smoothness of physicochemical trendlines going down (B-Al-)Sc-Y-La is better than that going down (B-Al-)Sc-Y-Lu.

Re: And it's literally been known since 1915 (Biron's secondary periodicity) that groups usually do not exhibit smooth trends, but display an alternation between even and odd periods. As Chistyakov noted, Sc-Y-Lu fits that, and Sc-Y-La doesn't.

Chistyakov's (1968) article is too short (2 pp.) and too selective to draw any conclusions from. Further, as with Jensen, Chistyakov only looked at one-half of the situation. Both authors failed to mention the fact that the trends going down Sc-Y-La were more like those going down -Ca-Sr-Ba and -K-Rb-Cs.

Re: Heavy alkaline earth metals are indeed somewhat like transition metals because they can use the d-orbitals (especially barium is quite adept at it). That is well-known by now. The difference is that they at least manage to use s-orbitals as well. That's not at all the same kind of situation as putting Lu in the f-block when it literally can't use f-orbitals for any chemistry.

Your point was that, "Lu cannot use f-orbitals whereas La can, making Lu obviously more like a transition metal." Here in, the same way that Ba is not more like a transition metal in its chemistry, neither is Lu more like a transition metal. --- Sandbh (talk) 02:11, 3 February 2024 (UTC)

References

Bünzli J & McGill I, Rare-earth elements. In: Elvers, B. (ed.) Ullmann’s Encyclopaedia of Industrial Chemistry, 7th edn, Wiley-VCH, Wiesbaden (2011) Clavaguéra C, Dognon J-P & Pyykkö P, Calculated lanthanide contractions for molecular trihalides and fully hydrated ions: The contributions from relativity and 4f-shell hybridization, Chemical Physics Letters, vol. 429, nos. 1–3, pp. 8–12 (2006) Cotton S, Lanthanide and Actinide Chemistry, Wiley, Chichester (2006) Gupta CK & Krishnamurthy N, Extractive Metallurgy of Rare Earths, CRC Press, Boca Raton (2005) Ji et al. 2015, Ionic bonding of lanthanides, as influenced by d- and f-atomic orbitals, by core-shells and by relativity, Journal of Computational Chemistry, 36(7), 449–458. doi:10.1002/jcc.23820 Jowsey J, Rowland RE & Marshall JH, The comparative deposition of yttrium, cerium, and thallium in bone tissue of dogs. In: Argonne National Laboratory, Radiological Physics Division Semiannual Report, July to December 1957, Illinois, 63–75 (1958) Langley RH, Structure and phase transitions of the lanthanide metals, Journal of Solid State Chemistry, vol. 38, no. 3, pp. 300–306 (1981) Liu R, Mao G & Zhang N, Research of chemical elements and chemical bonds from the view of complex network, Found. Chem., 21, 193–206 (2019) Marsh JK, The relation of yttrium to the lanthanons: A study of molecular volumes. J. Chem. Soc., 1084–1086 (1947) Mingos DMP, Essential Trends in Inorganic Chemistry, Oxford University Press, Oxford (1998) Ramakrishnan R, Matveev AV & Rösch N, The DFT + U method in the linear combination of Gaussian-type orbitals framework: Role of 4f orbitals in the bonding of LuF3, Chemical Physics Letters, vol. 468, nos. 1–3, pp. 158–161 (2009) Ratto CF, Coqblin B & d'Agliano EG 1969, Superconductivity of lanthanum and cerium at high pressures, Advances in Physics, vol. 18, pp. 489–513 Restrepo G, The periodic system: A mathematical approach, In: Scerri & Restrepo (2018) Roos et al. New relativistic atomic natural orbital basis sets for lanthanide atoms with applications to the Ce diatom and LuF3, Journal of Physical Chemistry A, vol. 112, no. 45, pp. 11431–11435 (2008) Russell AM & Lee KL, Structure-property relations in nonferrous metals, Wiley-Interscience, New York (2005) Scerri E & Restrepo G (eds.): Mendeleev to Oganesson: A Multidisciplinary Perspective on the Periodic Table, Oxford University Press, New York (2018) Scerri, E.R., Parsons, W.: What elements belong in Group 3 of the periodic table? In: Scerri, E., Restrepo, G. (eds.) Mendeleev to Oganesson: A multidisciplinary perspective on the periodic table, pp. 140–151. Oxford University Press, New York (2018) Steurer W & Dshemuchadse J, Intermetallics: Structures, properties, and statistics, Oxford University Press, Oxford (2016) Tibbetts TA & Harmon BN, "The electronic structure of Lu", Solid State Communications, vol. 44, no. 10, pp. 1409–1412 (1982) Vickery RC, The Chemistry of Yttrium and Scandium, Pergamon Press, New York (1960) Vickery RC, Scandium, yttrium, and lanthanum, In: Bailar Jr et al. (eds.), Comprehensive Inorganic Chemistry, vol. 3, pp. 329–354, Pergamon Press, Oxford (1973)

   

Density x EN

Electronegativity:		<1.9		≥1.9		(revised Pauling scale)
Density (g/cm3):	<7
	>7

Table

Metals and nonmetals by density and electronegativity

Density	Electronegativity (revised Pauling scale)
	< 1.9	≥ 1.9
< 7 gm/cm3	Groups 1 and 2 Sc, Y, La Ce, Pr, Eu, Yb Ti, Zr, V Al, Ga	Noble gases: He, Ne, Ar, Kr, Xe, Rn
		Halogen nonmetals: F, Cl, Br, I
		Unclassified nonmetals: H, C, N, P, O, S, Se
		Metalloids: B, Si, Ge, As, Sb, Te
> 7 gm/cm3	Nd, Pm, Sm, Gd, Tb, Dy Ho, Er, Tm, Lu; Ac–Es Hf, Nb, Ta; Cr, Mn, Fe, Co, Zn, Cd, In, Tl, Pb	Ni, Mo, W, Tc, Re Platinum group metals Coinage metals Hg, Sn, Bi, Po, At
H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Ra                                                                                                                                                 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Ac Th Pa U Np Pu Am Cm Bk Cf Es

DS

Thank you Double sharp. That was a good read.

1. Re, "there really isn't any good physical or chemical case for La under Y", good physical and chemical arguments in support of La in group 3 are set out in doi:10.1007/s10698-020-09384-2 (19 citations) and in Vernon R 2023, The location and composition of Group 3: A follow-on examination, ChemRxiv (235 views, 249 downloads).

2. Regarding the actinides, and any possible intention of matching the chemistry of the lanthanoids, Scerri (2021, p. 132) noted that the level at which a science operates is a question for its practitioners and the deepest most fundamental bases are not necessarily the best for all purposes. That is to say, it does not matter that the actinides have a more complex chemstry than the lanthanides. In any event, the An (and Ln) are united by all of them being known in the +3 oxidation state.

3. No, the situation for group 3 is not different from the situation with H and He. It all comes down to the perspective of interest.

Density of fcc metallic At (conjectures)

1. Iodine at 53 GPa adopts a metalic FCC structure, with a volume (Å/atom) of 19.91 (doi:10.1103/physrevb.49.3725, p. 3727). Such a stucture has a packing efficiency of 74%.

The volume of one mole of such iodine atoms is 19.91 x 10^–24 x 6.022 x 10²³ = 11.99 cc.

Since the atomic weight of iodine is 126.9 this suggests a density of 0.74 x 126.9/11.99 = 7.83 gm/cc, compared to 4.93 gm/cc for ordinary iodine. Thus, the density from orthorhombic to fcc iodine increases 1.58 times.

If this occurs for fcc astatine, it suggests a density of 6.2–6.5 x 1.58 = 10.03±0.24 gm/cc. The figure of 6.2–6.5 is from doi:10.1021/j150609a021, pp. 1182. 1185.

2. Another way to look at this is the metallization collapse that occurs when R/V = 1. Here, R = molar refractivity and V = molar volume. Pauling pointed out that the cube root of molar refractivity is tantamount to an approximate measure of the radius of the outermost valence electrons in the atom. The orbital radius of At is 114.6 pm. Cubed, this yields an R value value of 15.05 cc which is ≈ to V. The density is then the atomic weight of At = 210 divided by the molar volume of 11.137 cc = 13.96 x 0.74 packing efficiency = 10.33 gm/cc.

3. "From the known atomic or molecular dipole polarizabilities, we can estimate the atomic densities required to form metallic solids as a consequence of an emerging polarization catastrophe. As these polarizabilities increase monotonically proceeding down the halogen group, the estimated compressions necessary for metallization decrease monotonically" (doi:10.1103/PhysRevLett.111.116404, p. 2). The polarizability for I is 32.9± atomic units and that for At is 42.2±4. On this basis the density of At is 42.2/32.9 x 7.83 (fcc I density) = 10.04 gm/cc.

Nonmetal history of discovery

Nonmetals in the periodic table

Hydrogen

Helium

Lithium

Beryllium

Boron

Carbon

Nitrogen

Oxygen

Fluorine

Neon

Sodium

Magnesium

Aluminium

Silicon

Phosphorus

Sulfur

Chlorine

Argon

Potassium

Calcium

Scandium

Titanium

Vanadium

Chromium

Manganese

Iron

Cobalt

Nickel

Copper

Zinc

Gallium

Germanium

Arsenic

Selenium

Bromine

Krypton

Rubidium

Strontium

Yttrium

Zirconium

Niobium

Molybdenum

Technetium

Ruthenium

Rhodium

Palladium

Silver

Cadmium

Indium

Tin

Antimony

Tellurium

Iodine

Xenon

Caesium

Barium

Lanthanum

Cerium

Praseodymium

Neodymium

Promethium

Samarium

Europium

Gadolinium

Terbium

Dysprosium

Holmium

Erbium

Thulium

Ytterbium

Lutetium

Hafnium

Tantalum

Tungsten

Rhenium

Osmium

Iridium

Platinum

Gold

Mercury (element)

Thallium

Lead

Bismuth

Polonium

Astatine

Radon

Francium

Radium

Actinium

Thorium

Protactinium

Uranium

Neptunium

Plutonium

Americium

Curium

Berkelium

Californium

Einsteinium

Fermium

Mendelevium

Nobelium

Lawrencium

Rutherfordium

Dubnium

Seaborgium

Bohrium

Hassium

Meitnerium

Darmstadtium

Roentgenium

Copernicium

Nihonium

Flerovium

Moscovium

Livermorium

Tennessine

Oganesson

Most nonmetallic elements were discovered after the freezing of mercury in 1759 by the German-Russian physicist Josef Adam Braun and the Russian polymath Mikhail Lomonosov. Before then, carbon, sulfur and antimony were known in antiquity. Arsenic and phosphorus were discovered in the middle ages and in the Renaissance, respectively. In the ensuing century and a half, from 1766 to 1895, all the remaining nonmetallic elements, bar radon had been isolated. The latter three were discovered in 1898.

Antiquity

Carbon (C) and sulfur (S) were known in antiquity.

The earliest known use of charcoal dates to around 3750 BCE. The Egyptians and Sumerians employed it for the reduction of copper, zinc, and tin ores in the manufacture of bronze. Diamonds were probably known from as early as 2500 BCE. The first true chemical analyses were made in the 18th century; Antoine Lavoisier recognized carbon as an element in 1789.

Sulfur usage dates from before 2500 BCE; it was also recognized as an element by Lavoisier, in 1777.

17th century

Phosphorus (P) was prepared from urine, by Hennig Brand, in 1669.

18th century

Henry Cavendish, in 1766, was the first to distinguish hydrogen (H) from other gases, although Paracelsus around 1500, Robert Boyle (1670), and Joseph Priestley (?) had observed its production by reacting strong acids with metals. Lavoisier named it in 1793.

Carl Wilhelm Scheele obtained oxygen (O) by heating mercuric oxide (HgO) and nitrates in 1771, but did not publish his findings until 1777. Priestley also prepared this new "air" by 1774, but only Lavoisier recognized it as a true element; he named it in 1777.

Ernest Rutherford discovered nitrogen (N) while he was studying at the University of Edinburgh. He showed that the air in which animals breathed, after removal of exhaled carbon dioxide (CO₂), was no longer able to burn a candle. Scheele, Cavendish, and Priestley also studied this element at about the same time; Lavoisier named it in 1775 or 1776.

In 1774, Scheele obtained chlorine (Cl) from hydrochloric acid (HCl) but thought it was an oxide. Only in 1808 did Humphry Davy recognize it as an element.

Early 19th century

Iodine (I) was discovered in 1811 by Bernard Courtois from the ashes of seaweed.

In 1817, when Jöns Jacob Berzelius and Johan Gottlieb Gahn were working with lead (Pb) they discovered a substance that was similar to tellurium (Te). After more investigation Berzelius concluded that it was a new element, related to sulfur and tellurium. Because tellurium had been named for the Earth, Berzelius named the new element "selenium" (Se), after the moon.

Antoine Jérôme Balard and Leopold Gmelin both discovered bromine (Br) in the autumn of 1825 and published their results in the following year.

Late 19th century

In 1868, Pierre Janssen and Norman Lockyer independently observed a yellow line in the solar spectrum that did not match that of any other element. In 1895, in each case at around the same time, William Ramsay, Per Teodor Cleve, and Abraham Langlet independently observed helium (He) trapped in cleveite.

André-Marie Ampère predicted an element analogous to chlorine obtainable from hydrofluoric acid (HF), and between 1812 and 1886 many researchers tried to obtain it. Fluorine (F) was eventually isolated in 1886 by Henri Moissan.

Lord Rayleigh and Ramsay discovered argon (Ar) in 1894 by comparing the molecular weights of nitrogen prepared by liquefaction from air, and nitrogen prepared by chemical means. It was the first noble gas to be isolated. Lord Rayleigh would receive the Nobel Prize in Physics for "for his investigations of the densities of the most important gases and for his discovery of argon in connection with these studies".

In 1898, within a period of three weeks, Ramsay and Travers successively separated krypton (Kr), neon (Ne) and xenon (Xe) from liquid argon by exploiting differences in their boiling points.

20th century

In 1899, Rutherford and Robert B. Owens discovered a radioactive gas resulting from the radioactive decay of thorium (Th); Ramsay and Robert Whytlaw-Gray subsequently isolated radon (Rn) in 1910.

References

Category:Nonmetals Category:Chemistry Category:History of chemistry

History metalloids

Newth says that the following elements encompass metalloid and nonmetals: As, B, Br, C, Cl, F, H, I, N, O, P, Se, Si, S, Te.

Friend

The difficulty of drawing a dividing line between metals and non-metals is clearly shown by the existence of an alternative method of classifying the elements, which divides them into three groups, namely, non-metals, metalloids, and metals. A metalloid is an element which, although it resembles a metal in most characteristics, yet lacks some one or more of the features which typical metals generally present. Usually, the metalloids possess the form or appearance of metals, but are more closely allied to the non-metals in their chemical behaviour. The following elements are included in the metalloids : a hydrogen, tellurium, germanium, tin, titanium, zirconium, arsenic, antimony, bismuth, vanadium, columbium, tantalum, molybdenum, tungsten, and uranium.

@Double sharp: Berzelius, in 1818, thought Se was a metal due to its lustre. He further ascertained that it was acidifiable. I guess Dumas (1828) was still going by Berzelius's classification, and that by 1844, Dupasquier (among others) had worked it out.

Germanium has a record of being regarded as a poorly conducting metal, with its conductivity arising from impurities. AFAIK its status as a nonmetallic element was not sorted out until the 1930's(?) when the physics of semiconductors emerged. Curiously there is this:

"Germanium, Ge, a new nonmetallic[sic] element…" (Winkler 1886)

--- Winkler C (1886), Berichte der Deutschen Chemischen Gesellschaft, vol. 19, pp. 210–211

Arsenic and antimony have a long history of causing difficulties for classification science. The oldest quote I have for As is:

"Arsenic is in the main, however, an acid-forming element and plays the part of a non-metal in its compounds."

--- Schrader FC, Stone RW & Sanford S 1917, Useful minerals of the United States, Bulletin 624, United States Geological Survey, Washington

The oldest quote I have for Sb is:

"Antimony…is of more metallic appearance than arsenic, but, although it has some of the properties of the metals (lustre, electrical and thermal conductivity), in its chemical behaviour it is closely connected with arsenic and phosphorus…Bismuth…has no non-metallic characters [sic] and may be considered as a metal, as it forms no gaseous hydrogen derivative and its oxide has basic characteristics." (Molinari 1920, pp. 426, 792)

--- Molinari E 1920, Treatise on general and industrial inorganic chemistry, 2nd ed., J & A Churchill, London.

I suspect Te may have ended up with an "-ium" suffix due to it appearing to Müller (1783) to form a metallic alloy with gold, as AuTe₂, bearing in mind the limited understanding of time as to the distinction between metals an nonmetals.

*     *     *

In 1864, calling nonmetals "metalloids" was still sanctioned "by the best authorities" even though this did not always seem appropriate. The greater propriety of applying the word metalloid to other elements, such as arsenic, had been considered.

--- The Chemical News and Journal of Physical Science 1864, Notices of books: Manual of the metalloids, Jan 9, p. 22

As late as 1888, classifying the elements into metals, metalloids, and nonmetals, rather than metals and metalloids, was still regarded as peculiar and potentially confusing.

--- The Chemical News and Journal of Physical Science 1888, Books received: The students' hand book of chemistry, Jan 6, p. 11

In 1894 (Newth) and 1914 (Friend) noted the metalloids have a predominately nonmetallic chemistry.

--- Newth GS 1894, A Text-book of Inorganic Chemistry, Longmans, Green, and Co, London, pp. 7−8

--- Friend JN 1914, A Text-book of Inorganic Chemistry, vol. 1. Charles Griffin and Company, London, p. 9: “Usually, the metalloids possess the form or appearance of metals, but are more closely allied to the non-metals in their chemical behaviour.”

Use of the word "metalloid" (for in-betweens) didn't take off until post-1947 when Pauling wrote in his classic and influential textbook, General chemistry: An introduction to descriptive chemistry and modern chemical theory. He described them as "elements with intermediate properties ... occupy[ing] a diagonal region [on the periodic table], which includes boron, silicon, germanium, arsenic, antimony, tellurium, and polonium."

Metalloid reactivity

   the highly to moderately reactive halogen nonmetals—fluorine, chlorine, bromine and iodine;

   a set of unclassified nonmetals, of high to low reactivity, encompassing elements like hydrogen, carbon, nitrogen, and oxygen, for which there is no widely recognized collective name; and

   the metalloid elements, none being particularly reactive, and which are considered either as nonmetals or as a third category distinct from metals and nonmetals.

"Crystalline boron is relatively inert"; silicon "is generally highly unreactive"; "germanium is a relatively inert semimetal"; "pure arsenic is also relatively inert"; "metallic antimony is ... inert at room temperature"; "compared to S and Se, Te has relatively low chemical reactivity."

• Reid R 2018, Inorganic Chemistry, Ed-Tech Press, Waltham Abbey Essex, ISBN 978-1-83947-198-8
• Graves Jr JL 2022, A Voice in the Wilderness: A Pioneering Biologist Explains How Evolution Can Help Us Solve Our Biggest Problems, Basic Books, New York, ISBN 978-1-6686-1610-9,
• Hill G 1997, GCSE science, 2nd ed., Letts Educational, London, ISBN 978-1-85758-592-6
• Rosenberg E 2013, Germanium-containing compounds, current knowledge and applications, in Kretsinger RH, Uversky VN & Permyakov EA (eds), Encyclopedia of Metalloproteins, Springer, New York, doi:10.1007/978-1-4614-1533-6_582
• Obodovskiy I 2015, Fundamentals of Radiation and Chemical Safety, Elsevier, Amsterdam, ISBN 978-0-12-802026-5
• Orisakwe OE 2012, Other heavy metals: antimony, cadmium, chromium and mercury, in Pacheco-Torgal F, Jalali S & Fucic A (eds), Toxicity of Building Materials, Woodhead Publishing, Oxford, pp. 297-333, doi:10.1533/9780857096357.297
• Yin et al. 2018, Hydrogen-assisted post-growth substitution of tellurium into molybdenum disulfide monolayers with tunable compositions, Nanotechnology, vol. 29, no 14, item 145603 (9pp), doi:10.1088/1361-6528/aaabe8

Comparable metals

In a periodic table context, metals display a similar range of reactivity. Highly to fairly reactive metals, such as sodium and uranium, are found in the s- and f-blocks on the left side of the table (and below its main body). In the middle are d-block metals, such as scandium, iron and nickel, of high to low reactivity. To the right are p-block metals such as tin and lead, none being particularly reactive. The least reactive ("noble") metals, such as platinum and gold, are clustered in an island within the d-block.

Complements

Well, there is a long history in the literature of similarly described types of metals and nonmetals, ranging from highly reactive metals to less reactive metals, even noble metals, and then transitioning through metalloids, moderately active nonmetals, highly reactive nonmetals and culminating in the noble gases.

• 1. "What, in general, is the difference between active metals, less active metals, less active non-metals, active non-metals, and inert gases…?"

--- Friedenberg EZ 1946, A Technique for developing courses in physical science adapted to the needs of students at the junior college level, University of Chicago, Chicago

• 2. "Between Groups I and VII there are gradations from active metals (Col. I) to less active metals to moderately active nonmetals to volatile nonmetals (halogens Col. VII)." (Perlman 1970, p. 439)

--- Perlman JS 1970, The atom and the universe, Wadsworth Publishing, Belmont, California

• 3. "As one examines the elements…a progression is observed from slightly nonmetallic to strongly nonmetallic and very active." (Stafford et al. 1977, p. 225)

--- Stafford DG, Renner JW & Rusch JJ 1977, The physical sciences: inquiry and investigation, Glencoe Press, Beverly Hills

• 4. "There are groups of elements that have similar properties, including highly reactive metals, less-reactive metals, highly reactive nonmetals (such as chlorine, fluorine, and oxygen), and some almost completely nonreactive gases (such as helium and neon)."

--- American Association for the Advancement of Science, 1993, Benchmarks for Science Literacy, Oxford University Press, New York, p. 78

• 5. "Between the "virulent and violent" metals on the left of the periodic table, and the "calm and contented" metals to the right are the transition metals, which form "a transitional bridge between the two" extremes. (Atkins 2001, pp. 24–25)

--- Atkins PA 2001, The periodic kingdom: A journey into the land of the chemical elements, Phoenix, London

• 6. "Describe how groups of elements can be classified including highly reactive metals, less reactive metals, highly reactive nonmetals, less reactive nonmetals, and some almost completely nonreactive gases."

--- Padilla MJ, Cyr M & Miaoulis I 2005, Science explorer (Indiana Grade 6), teachers's edition, Prentice Hall, Upper Saddle River, New Jersey, p. 27

• 7. "Grade 7: While engaged in tasks that address the structure and properties of matter, the student demonstrates an understanding of important information, such as distinctions between various ways elements can be grouped (highly reactive metals, less reactive metals, highly reactive nonmetals, almost completely nonreactive gases) (e.g., explaining the differences between two ways that elements can be grouped—for example, describing how highly reactive metals differ from less reactive metals)."

--- Marzano RJ & Haystead MW 2008, Making Standards Useful in the Classroom, Association for Supervision and Curriculum Development, Alexandria, VA, p. 211

• 8. "The elements change from ... metalloids, to moderately active nonmetals, to very active nonmetals, and to a noble gas."

--- Welcher SH 2009, High marks: Regents Chemistry Made Easy, 2nd ed., High Marks Made Easy, New York,

• 9. "Elements to the left of the zigzag line are all, at least marginally, metallic. Elements to the right of the same line are all at least marginally nonmetallic." (Dougherty & Kimel 2012, p. 48)

--- Dougherty R & Kimel JD 2012, Superconductivity revisited, CRC Press, Boca Raton

• 10. "... with "no-doubt" metals on the far left of the table, and no-doubt non-metals on the far right ... the gap between the two extremes is bridged first by the poor metals, and then by the metalloids—which, perhaps by the same token, might collectively be renamed the "poor non-metals".

--- Dingle A 2017, The Elements: An Encyclopedic Tour of the Periodic Table, Quad Books, Brighton, p. 101

• 11. "Those [elements] classified as metallic range from the highly reactive sodium and barium to the noble metals, such as gold and platinum. The nonmetals…encompass…the aggressive, highly-oxidizing fluorine and the unreactive gases such as helium."

--- Overton et al. 2018, Inorganic Chemistry, 7th ed., Oxford University Press, Oxford, preface

A similar pattern occurs along the periods:

• 12. "Across each period is a more or less steady transition from an active metal through less active metals and weakly active non metals to highly active nonmetals and finally to an inert gas."

--- Beiser A 1968, Perspectives of modern physics, McGraw-Hill, New York

• 13. "A period represents a stepwise change from elements strongly metallic to weakly metallic to weakly nonmetallic to strongly nonmetallic, and then, at the end, to an abrupt cessation of almost all chemical properties." (Booth & Bloom 1972, p. 426)

--- Booth VH & Bloom ML 1972, Physical science: a study of matter and energy, Macmillan, New York

Types

Types of nonmetals and metals, their average electronegativity values, and electronegativity distributions arbitrarily divided into 0.5 spans (for the first 102 elements). For the types of nonmetals, there is a progression from less electronegative to more electronegative. A similar progression occurs for the types of metals. The transition metal values exclude those of the noble metals.

A broadly comparable range of types occurs among the metals, from highly reactive to less reactive (even noble). On the left side of the periodic table, and below its main body, are highly to fairly reactive s- and f-block metals such as sodium, calcium and uranium. Towards the middle of the periodic table are transition metals, such as scandium, iron and nickel, of high to low reactivity. To the right of the transition metals, from group 13 onwards, are p-block metals such as tin and lead, none of which are particularly reactive. A subset of the transition metals (including platinum and gold) are referred to as noble metals on account of their reluctance to engage in chemical activity.

Pairs

For comparative purposes, the metals range from highly reactive to less reactive (even noble). On the left side of the periodic table are very active metals, such as sodium and calcium. Towards the middle of the periodic table are transition metals, such as iron and chromium, which (mostly) have moderate to low reactivity. To the right of the transition metals are the post-transition metals, such as tin and lead, none of which are particularly reactive. A subset of the transition metals, including platinum and gold, are referred to as noble metals on account of their reluctance to engage in chemical activity.

A broadly comparable range of types occurs among the metals, from highly reactive to less reactive (even noble). On the left side of the periodic table, and below its main body, are highly to fairly reactive metals, such as sodium, calcium, and uranium. Towards the middle of the periodic table are transition metals, such as scandium, iron and nickel, of high to low reactivity. To the right of the transition metals, (from group 13 onwards) are metals such as tin and lead, none of which are particularly reactive. A subset of the transition metals including platinum and gold, are referred to as noble metals on account of their reluctance to engage in chemical activity.

More pairs

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NG/NM comparisons

• I think my recent addition to the 1st paragraph on the section includes all that is needed about noble gases.
• Do the sources for the 1st sentence in the comparison all say this comparison is “commonly drawn”? Or is “commonly” justified by the fact that three sources are listed?
• The other two sentences of the comparison paragraph essentially compare a specific NG (Xe) and a specific NM (Os) - hardly significant enough to include in a general article about nonmetals. What’s left is just a statement that both categories are unreactive and that is adequately covered in the first paragraph. So I think this paragraph should be removed.
• The comparison - with or without its paragraph - hardly deserves to be elevated in importance by using a paired illustration. Better to show just an example of a NG.

YBG (talk) 06:24, 27 October 2023 (UTC)

I do agree that the Xe-Os comparison could be removed. It is not really about the pairing, but is merely a case of a secondary relationship. Both elements have eight valence electrons over an inert core. In that sense it is like Cl-Mn (replace eight with seven), which does not fit the set of pairings too well. Double sharp (talk) 09:51, 27 October 2023 (UTC)

@Double sharp would you favor removing the first sentence also and not just the Xe-Os comparison? If so, do you think that the mention of gold and platinum should be added to the first paragraph if the section? YBG (talk) 15:30, 27 October 2023 (UTC)

@YBG: Well, I just had the chance to look at Holleman & Wiberg. They compare noble gases to noble metals in the sense that one is group VIIIA, and the other is group VIIIB. It's part of a general comparison of main-group vs transition elements. So okay, there is a similarity, but for them it is not part of the full category-by-category set. Given that, I think I'd rather restrict it to what you suggested, indeed. Double sharp (talk) 16:02, 27 October 2023 (UTC)

In my opinion, incidentally, the mention of Xe intermetallics is misplaced here. It is not really about the noble gases, but rather it is about how metallicity, or lack thereof, inherently depends on pressure. So it should rather be part of a general discussion of what happens at high pressure, like we have that deep down. Yes, all elements eventually become metals, but there is sometimes weirdness along the way (Na first de-metallises before re-metallising). Double sharp (talk) 16:09, 27 October 2023 (UTC)

@YBG and Double sharp:

Recent 1st para. additions. With respect YBG, the recent additions to the first paragraphs of noble gases and halogen nonmetals have thrown out the structure of the sub-section. Comparative comments about each of the four types of nonmetal are made in the penultimate paragraph of each sub-section. For now, I've therefore reverted these edits.

Commonly drawn comparison? It's been drawn from as early as 1924, and continues to be drawn. While I haven't kept track of all the sources that I stumbled upon saying so, here are some of them:

Noble metals/noble gases

The inclusion of the "noble gases" and the "noble metals" in the same periodic group 8, is therefore necessitated in the classification of the elements according to chemical properties and according to atomic structure. Mendeleef’s division of the “long periods” into even and odd series of over fifty years ago is today abundantly justified, and, though he later failed to appreciate the close relation between the “noble metals” and the “noble gases”… — Main Smith JD 1924, Chemistry & Atomic Structure, Ernnest Benn Ltd., London, p. 78 Gold is not acted upon by air or oxygen at any temperature, hence the alchemists called gold a noble metal in contrast with base metals—like copper, lead, tin, etc. — which are oxidized and lose their metallic character when heated in air. Silver and platinum are noble metals for the same reason as gold. The inert gases argon and its congeners have been called noble gases because they are chemically inactive. — Mellor JW 1927, Modern Inorganic Chemistry, Longmans, Green and Co., London, p. 460 The eighth vertical series is, however, remarkable in one aspect, in that its two natural families are the inert gases and the nine metals of the iron-platinum family. At first sight no two families of elements could appear more dissimilar, and yet popular phraseology has seized on one point of resemblance. For the former family is often spoken of as the "noble gases" ("Edelgasen"), whereas the platinum sub-family is generally referred to as the "noble metals," with the inclusion of gold from the currency group. In the opinion of hardworking chemists, the badge of nobility seems to be idleness and detachment from ordinary mundane matters. To this ideal the inert gases - the key elements thoroughly conform in all readily realisable circumstances. They are the "rois fainéants" of the chemical elements. Under ordinary atmospheric conditions the noble metals display considerable chemical activity, although it is significant that this power of combination is manifested mainly in their co-ordination compounds, whence it may be deduced that a considerable part of the chemical affinity is supplied by electrons derived entirely from the associating addenda, which thus conduce to the stability of the resulting compounds. At temperatures round about the melting point of lead most of the chemical energy of the platinum metals has already disappeared, and nearly all their compounds would have undergone thermal decomposition. If we could habitually live under such conditions we should experience very little reluctance in linking together in one group of inert elements the noble gases and the noble metals. Moreover, some four members of the eighth metallic series give rise to volatile carbonyls in which the metallic atom appears not actively to contribute electrons, but to receive them passively from the various proportions of carbon monoxide, which go to form these remarkable metallic carbonyls (see pages 351). Again it will be noted in the chapter on intermetallic compounds (page 336) that the Hume-Rothery rule giving simple ratios between the total number of valency electrons and total number of atoms in the molecule is valid for the alloys of iron, cobalt, nickel and palladium only if these metals contribute no electrons, or, in other words, have zero valency. Accordingly these passive attributes of the eighth family of metals afford some justification for their inclusion in the same periodic series as the inert gases. — Morgan GT & Burtsall FH 1936, Inorganic Chemistry: A Survey of Modern Developments, W Heffer & Sons, Cambridge, p.256–257 The alchemists called gold, platinum and other metals that are resistant to acids and to oxygen the "noble metals". Following this nomenclature, chemists call helium, neon and other inert gases the noble gases. — Gordon NE & Trout WE 1940, Introductory College Chemistry, John Wiley & Sons, New York, p. 371 With the exception of the 'noble gases', helium and its relatives, and the 'noble metals', gold and platinum, etc., we rarely find atoms existing as collections of single atoms. Swanson MA 1959, Scientific Epistemologic Backgrounds of General Semantics: Lectures on Electro-colloidal Structures, Institute of General Semantics, Lakeville, CT, p. 29 ... Most chemists began to refer to the family as the noble gases' just as the rather unreactive and chemically aloof elements such as gold and platinum are referred to as the noble metals.  — Wood JH, Keenan CW & Bull WE 1968, Fundamentals of College Chemisty, 2nd ed., Harper International, New York The gases are called the "noble" gases, in recognition of their low reactivity, which parallels that of the "noble" metals. — Eastman RH 1970, General Chemistry: Experiment and Theory, Holt, Rinehart and Winston, New York, p. 455 Early chemists called gold, silver, and platinum, which were rather unreactive with other elements, the noble metals. So it seemed appropriate to call these, by analogy, the noble gases. — Fuller EC 1974, Chemistry and Man's Environment, Houghton Mifflin, Boston, p. 194, ISBN 978-0-395-17086-1 Use of the terms transition or transitional elements … were originally applied solely to the group VIII triads (i.e., Fe-Co-Ni in period 4, Ru-Rh-Pd in group 5, and Os-lr-Pt in period 6) … These elements were very similar in their ... chemical properties ... and frequently resisted attack by common reagents (hence the name noble metal for the heavier members). When the rare or noble gases were later discovered, it was suggested that they too were transition elements, as they also bridged the gap between successive cycles of increasing maximum oxidation states. Indeed, they were considered to be more perfect examples of transitional species as the contrast between the elements at the end and beginning of successive periods (e.g., CI(VII) and K(I)) was much sharper than that between elements at the beginning and end of successive series (e.g., Mn(VII) and Cu(I)), and the transition occurred in these cases in one step rather than three. Finally, the noble gases appeared to be chemically inert, and thus represented truly "noble" elements, in contrast to the known reactivity of the so-called noble metals. This view of the group VIII triads as imperfect "noble gases" was also used by later writers on the periodic table and the observation that they should really be extended to transitional tetrads by incorporating Cu, Ag, and Au was first pointed out by Jorgensen. — Jensen WB 1986, "Classification, symmetry, and the periodic table," Computers & Mathematics with Applications, vol. 12B (1−2), pp. 487−510 (496), doi:10.1016/0898-1221(86)90167-7 Emphasis has been placed on the chemistry of elements which are most resistant to oxidation, such as the noble metals and the noble gases." — Banks RE 2000, Fluorine Chemistry at the Millennium: Fascinated by Fluorine, Elvesier Science, Kidlington, Oxford, ISBN 978-0-08-043405-6, p. 60 The name 'noble gases' has been chosen to replace 'inert gases'. It is reminiscent of the name 'noble metals' (for metals such as gold and platinum that do not react readily. — Clugston M & Flemming R 2000, Advanced Chemistry, Oxford University Press, Oxford, ISBN 978-0-19-914633-8, p. 354 In place of the noble gases, the transition metal grouping has the noble metals. — Wiberg N 2001, Inorganic Chemistry, Academic Press, San Diego, ISBN 978-0-12-352651-9 Noble gases ... The name comes from the same root as noble metals. — Ede AG 2006, The Chemical Element: A Historical Perspective, Greenwood Press, Westport CT, ISBN 978-0-313-33304-0, p. 163 It is rare to find elements in nature in pure form ... There are some exceptions. however ... these metals are sometimes called the noble metals since they have a low reactivity. The noble gases are also not reactive and can be found in nature in uncombined form. — Hein M & Arena S 2011, Foundations of College Chemistry, 13th ed., John Wiley & Sons, Hoboken, New Jersey, ISBN 978-0470-46061-0, p. 50 Noble metals and noble gases do not easily enter chemical reactions with other elements. — Pulaczewska H 2011, Aspects of Metaphor in Physics: Examples and Case Studies, De Gruyter, Berlin, ISBN 978-3-484-30407-9, p. 262 The 'noble' metals are unreactive -- echoing the inert noble gases of group 18 ... and resistant to corrosion. — Green D 2016, The Periodic Table in Minutes, Quercus, London, ISBN 978-1-78429-605-6, p. 130 The start of noble gas chemistry in 1962 [occurred] with the help of a noble metal, platinum ... Interestingly, two nobles [noble metal and noble gas] make so strong [a] bond…that some of them reach the covalent limit. Gold is really a golden candidate to form a chemical bond with a noble gas atom due to relativistic contraction in radius and subsequent enhancement in electronegativity. Gold has the highest capability to form strong bond with noble gas atoms followed by copper and silver.  — Pan et al. 2019, "Noble-noble strong union: Gold at its best to make a bond with a noble gas atom", ChemistryOpen, February, pp. 173–187, doi:10.1002/open.201800257 Noble gases ... do not readily react ... like the noble metals they resist undergoing chemical reactions, but they can react in the right circumstances. — Barton A 2021, States of Matter, States of Mind, CRC Press, Boca Raton, ISBN 978-0-429-33290-6, p. 182

There are some other considerations.

• The start of noble gas chemistry in 1962 occurred with the help of a noble metal, platinum, albeit no Pt-Xe bond was involved.
• The field of noble gas-noble metal chemistry, which began in 1977, experienced a renaissance in 2000. While the focus of the linked article is to Cu, Ag and Au, there are mentions of other NM-NG compounds in the literature.

Xe-Os comparison. I included this in order to add "color" and interest to the paragraph. Scerri mentions it in his The Periodic Table: Its Story and Significance (2020, p. 411) as follows, "As Geoffrey Rayner Canham, a leading advocate of teaching inorganic chemistry in a qualitative manner, has written, the similarities shown far exceed any expectations on electronic grounds."

Paired illustrations. I've replaced all these with single images.

Taking into account the repeated comparisons made between noble gases and noble metals since 1924, and the ongoing interest in noble gas-noble metal chemistry I feel it is reasonable to

Group 17/1 comparisons

• I think my recent addition to the 1st paragraph includes all that is needed about alkali metals.
• In keeping with the name halogen and the content of the first paragraph, I think a good illustration would have a picture with sodium metal on the left, chlorine gas on the right and a pile of table salt (or a salt shaker) in the center, with Na, NaCl, and Cl in the caption or even better in the pic itself.
• The most salient parts of the comparison paragraph have been incorporated into the first paragraph. The only significant fact not in that paragraph is the common ability of group 1 and 17 to form -1 ions. I don’t think that is very significant in the context of a general article about nonmetals, and so I think that whole paragraph should be deleted.

YBG (talk) 06:24, 27 October 2023 (UTC)

I can agree with this, since −1 anions are not too characteristic of alkali metals even though they are mostly possible (for Li it is not even known yet, IIRC). Probably Au with actual aurides is a better comparison to the halogens, though off the top of my head I can't remember if it's been done in RS. Double sharp (talk) 16:05, 27 October 2023 (UTC)

@YBG and Double sharp: Thanks.

I've previously addressed the 1st para., and mentioned the removal of all the image pairs.

Regarding −1 alkalide anions, the context is:

1. Nonmetals cannot be understood without appreciating metals i.e. the name "nonmetal" includes the term "metal". Please further see the two tables of comparative properties at the end of the article, both of which include a metals column.
2. As noted, many nonmetallic elements have some metallic aspects; and many metallic elements (including e.g. Au) have some nonmetallic aspects. Hence the comparison with metals is relevant and fruitful.
3. The synthesis of a crystalline salt of the sodium anion Na^– was reported in 1974. It represented the second major overturning of conventional wisdom (Dye at al. 2006, p. 206), the first being the preparation of a noble gas compound in 1962. Since then further compounds (“alkalides”) containing anions of the other alkali metals (bar Li and Fr) as well as that of Ba(!), have been prepared.
4. I feel that the existence of −1 alkalide anions is a noteworthy and interesting illustration of items 1 and 2.

Dye et al. 2006, "Role of cation complexants in the synthesis of alkalides and electrides", Advances in Inorganic Chemistry, 205–231. doi:10.1016/s0898-8838(06)59006-3

---

• The quote box would be a great quote IF the subject of this section were the comparison of groups 1&17 - or IF the subject were L-R PT trends. But it is neither. The subject of this section is halogen nonmetals as a type of nonmetal. Better to find another article for this quote.
• Furthermore, having 5 elipses and one bracketed addition in a relatively short quote seems problematic. Just how much was left out?
• Finally, when a section has a pic, a high bar must be reached to also have a quote box. That bar is far from met. Best to drop the quote box.

YBG (talk) 06:24, 27 October 2023 (UTC)

Here's the background to mentioning metals in an article about nonmetals:

1. Nonmetals are one of the two great divisions of the periodic table, the other being the metals.
2. One cannot understand nonmetals without appreciating metals i.e. the name "nonmetal" includes the terms "metal".
3. As noted, many nonmetallic elements are said to have some metallic aspects; and many metallic elements have some nonmetallic aspects. Hence the comparison with metals is relevant and fruitful.
4. There is a long history of the idea of parallels among the elements between e.g. active metals, less active metals, less active nonmetals and active nonmetals.
5. The most stable compounds of nonmetals are those with metals, a classic example being NaCl.

As you say, the subject of the section is the halogens as a type of nonmetal.

As noted, the comparison of halogen nonmetals with alkali metals is part of Chemistry 101 rather then being too much in the weeds.

The paired picture happens to complement what the lede paragraph says:

"Although the halogen nonmetals are notably reactive and corrosive elements, they can be combined with equally reactive alkali metals to form relatively stable and unreactive chemical salts such as everyday toothpaste (NaF); table salt (NaCl); swimming pool disinfectant (NaBr); or food supplements (eg KI). The term "halogen" itself means "salt former".[142]"

It provides valuable context.

I've restored most of the quote. Here's a before and after comparison:

Before	After
We focus mainly on the gross structure ... metals are here ... non-metals are there, and so on ... Once [this is] grasped you can start to show that there's some order to it. We talk about the Group 1 alkali metals ... Then at the other extreme ... are the halogens. The idea that the table shows us how to group similar elements starts to come together in this way.[141]	We focus mainly on the gross structure – the metals are here, the non-metals are there, and so. Once they have grasped this, you can start to show that there’s some order to it. We talk about ... the alkali metals ... Then at the other extreme there are ... [the] halogens. The idea that the table shows us how to group similar elements starts to come together in this way.[141]

--- Sandbh (talk) 12:05, 28 October 2023 (UTC)

Noble

• The inclusion of the "noble gases" and the "noble metals" in the same periodic group 8, is therefore necessitated in the classification of the elements according to chemical properties and according to atomic structure. Mendeleef’s division of the “long periods” into even and odd series of over fifty years ago is today abundantly justified, and, though he later failed to appreciate the close relation between the “noble metals” and the “noble gases”…

— Main Smith JD 1924, Chemistry & Atomic Structure, Ernnest Benn Ltd., London, p. 78

• Gold is not acted upon by air or oxygen at any temperature, hence the alchemists called gold a noble metal in contrast with base metals—like copper, lead, tin, etc. — which are oxidized and lose their metallic character when heated in air. Silver and platinum are noble metals for the same reason as gold. The inert gases argon and its congeners have been called noble gases because they are chemically inactive.

— Mellor JW 1927, Modern Inorganic Chemistry, Longmans, Green and Co., London, p. 460

• Each period comprises eight groups, commencing with I and ending with VIII, the simple periods and the first sub-periods of the long periods terminating with inert or noble gases whereas the second sub-periods of the long periods terminate with noble metals.

— The Encyclopædia Britannica 1937, volume 17, p.520

• The gases are called the "noble" gases, in recognition of their low reactivity, which parallels that of the "noble" metals.

— Eastman RH 1970, General Chemistry: Experiment and Theory, Holt, Rinehart and Winston, New York, p. 455

• Early chemists called gold, silver, and platinum, which were rather unreactive with other elements, the noble metals. So it seemed appropriate to call these, by analogy, the noble gases.

— Fuller EC 1974, Chemistry and Man's Environment, Houghton Mifflin, Boston, p. 194, ISBN 978-0-395-17086-1

---

• Use of the terms transition or transitional elements … were originally applied solely to the group VIII triads (i.e., Fe-Co-Ni in period 4, Ru-Rh-Pd in group 5, and Os-lr-Pt in period 6) … These elements were very similar in their ... chemical properties ... and frequently resisted attack by common reagents (hence the name noble metal for the heavier members). When the rare or noble gases were later discovered, it was suggested that they too were transition elements, as they also bridged the gap between successive cycles of increasing maximum oxidation states. Indeed, they were considered to be more perfect examples of transitional species as the contrast between the elements at the end and beginning of successive periods (e.g., CI(VII) and K(I)) was much sharper than that between elements at the beginning and end of successive series (e.g., Mn(VII) and Cu(I)), and the transition occurred in these cases in one step rather than three. Finally, the noble gases appeared to be chemically inert, and thus represented truly "noble" elements, in contrast to the known reactivity of the so-called noble metals. This view of the group VIII triads as imperfect "noble gases" was also used by later writers on the periodic table and the observation that they should really be extended to transitional tetrads by incorporating Cu, Ag, and Au was first pointed out by Jorgensen.

— Jensen WB 1986, "Classification, symmetry, and the periodic table," Computers & Mathematics with Applications, vol. 12B (1−2), pp. 487−510 (496), doi:10.1016/0898-1221(86)90167-7

• Emphasis has been placed on the chemistry of elements which are most resistant to oxidation, such as the noble metals and the noble gases."

— Banks RE 2000, Fluorine Chemistry at the Millennium: Fascinated by Fluorine, Elvesier Science, Kidlington, Oxford, ISBN 978-0-08-043405-6, p. 60

• The name 'noble gases' has been chosen to replace 'inert gases'. It is reminiscent of the name 'noble metals' (for metals such as gold and platinum that do not react readily.

— Clugston M & Flemming R 2000, Advanced Chemistry, Oxford University Press, Oxford, ISBN 978-0-19-914633-8, p. 354

• In place of the noble gases, the transition metal grouping has the noble metals.

— Wiberg N 2001, Inorganic Chemistry, Academic Press, San Diego, ISBN 978-0-12-352651-9

• Noble gases ... The name comes from the same root as noble metals.

— Ede AG 2006, The Chemical Element: A Historical Perspective, Greenwood Press, Westport CT, ISBN 978-0-313-33304-0, p. 163

---

• It is rare to find elements in nature in pure form ... There are some exceptions. however ... these metals are sometimes called the noble metals since they have a low reactivity. The noble gases are also not reactive and can be found in nature in uncombined form.

— Hein M & Arena S 2011, Foundations of College Chemistry, 13th ed., John Wiley & Sons, Hoboken, New Jersey, ISBN 978-0470-46061-0, p. 50

• Noble metals and noble gases do not easily enter chemical reactions with other elements.

— Pulaczewska H 2011, Aspects of Metaphor in Physics: Examples and Case Studies, De Gruyter, Berlin, ISBN 978-3-484-30407-9, p. 262

• The 'noble' metals are unreactive -- echoing the inert noble gases of group 18 ... and resistant to corrosion.

— Green D 2016, The Periodic Table in Minutes, Quercus, London, ISBN 978-1-78429-605-6, p. 130

• The start of noble gas chemistry in 1962 [occurred] with the help of a noble metal, platinum ... Interestingly, two nobles [noble metal and noble gas] make so strong [a] bond…that some of them reach the covalent limit. Gold is really a golden candidate to form a chemical bond with a noble gas atom due to relativistic contraction in radius and subsequent enhancement in electronegativity. Gold has the highest capability to form strong bond with noble gas atoms followed by copper and silver. 

— Pan et al. 2019, "Noble-noble strong union: Gold at its best to make a bond with a noble gas atom", ChemistryOpen, February, pp. 173–187, doi:10.1002/open.201800257

• Noble gases ... do not readily react ... like the noble metals they resist undergoing chemical reactions, but they can react in the right circumstances.

— Barton A 2021, States of Matter, States of Mind, CRC Press, Boca Raton, ISBN 978-0-429-33290-6, p. 182

Outliers

Some elements widely regarded as either metals or other types of nonmetals have instead been less commonly counted as metalloids. Among the metals, aluminium and polonium (for example) have occasionally been so recognized. Examples of other types of nonmetals occaisionally having been recognized as metalloids include carbon and selenium.

Aluminium has some properties that are unusual for a metal; taken together, these are sometimes used as a basis to classify it as a metalloid. Its crystalline structure shows some evidence of directional bonding. Aluminium bonds covalently in most compounds. The oxide Al₂O₃ is amphoteric and a conditional glass-former. Aluminium can form anionic aluminates, such behaviour being considered nonmetallic in character.

Polonium shows nonmetallic character in its halides, and by the existence of polonides. The halides have properties generally characteristic of nonmetal halides (being volatile, easily hydrolyzed, and soluble in organic solvents). Many metal polonides, obtained by heating the elements together at 500–1,000 °C, and containing the Po²⁻ anion, are also known.

Graphite, the most stable form of carbon has a lustrous appearance and is a fairly good electrical conductor. Like a metal, the conductivity of graphite in the direction of its planes decreases as the temperature is raised; it has the electronic band structure of a semimetal. The allotropes of carbon, including graphite, can accept foreign atoms or compounds into their structures via substitution, intercalation, or doping. The resulting materials are referred to as "carbon alloys". Carbon can form ionic salts, including a hydrogen sulfate, perchlorate, and nitrate (C⁺
₂₄X⁻.2HX, where X = HSO₄, ClO₄; and C⁺
₂₄NO^–
₃.3HNO₃). In organic chemistry, carbon can form complex cations – termed carbocations – in which the positive charge is on the carbon atom; examples are CH⁺
₃ and CH⁺
₅, and their derivatives.

Its most stable form, the grey trigonal allotrope, is sometimes called "metallic" selenium because its electrical conductivity is several orders of magnitude greater than that of the red monoclinic form. The metallic character of selenium is further shown by its lustre, and its crystalline structure, which is thought to include weakly "metallic" interchain bonding. Selenium can be drawn into thin threads when molten and viscous. It shows reluctance to acquire "the high positive oxidation numbers characteristic of nonmetals". It can form cyclic polycations (such as Se²⁺
₈) when dissolved in oleums (an attribute it shares with sulfur and tellurium), and a hydrolysed cationic salt in the form of trihydroxoselenium(IV) perchlorate [Se(OH)₃]⁺·ClO^–
₄.

YBG3

Thanks YBG.

Could you kindly clarify what you meant by "the system as a whole ...[being] too novel to be prominently displayed"? At no time has the article displayed the system as a whole. Instead the parallels have been mentioned on a type basis.

While this is an article about nonmetals, many nonmetallic elements are said to have some metallic aspects; and many metallic elements have some nonmetallic aspects. Hence the comparison with metals is relevant and fruitful.

I've removed all the paired images except for the alkali metal-halogen image since this is Chemistry 101.

Please note that the text for each of the four types of nonmetals includes a reference to geographic analogies, which I've listed hereunder for convenience:

1. "An analogy can be drawn between the noble gases and noble metals such as platinum and gold, as they share a similar reluctance to combine with other elements.^[132] As a further analogy, xenon, in the +8 oxidation state, forms a pale yellow explosive oxide, XeO₄, while osmium, another noble metal, forms a yellow, strongly oxidizing oxide,^[133] OsO₄. Additionally, there are parallels in the formulas of the oxyfluorides: XeO₂F₄ and OsO₂F₄, and XeO₃F₂ and OsO₃F₂.^[134]"

2. "The highly nonmetallic halogens in group 17 find their counterparts in the highly reactive alkali metals, such as sodium and potassium, in group 1.^[149] Further, and much like the halogen nonmetals, most of the alkali metals are known to form –1 anions, a characteristic seldom observed among metals.^[150]"

3. "In the periodic table, to the left of the weakly nonmetallic metalloids are an indeterminate set of weakly metallic metals including tin, lead and bismuth,^[153] sometimes referred to as post-transition metals.^[154] Dingle explains the situation this way:

... with "no-doubt" metals on the far left of the table, and no-doubt non-metals on the far right ... the gap between the two extremes is bridged first by the poor (post-transition) metals, and then by the metalloids—which, perhaps by the same token, might collectively be renamed the "poor non-metals".[155]"

4. "There is a geographic analogy between the unclassified nonmetals and transition metals. The unclassified nonmetals are positioned between the strongly nonmetallic halogens on the right and the weakly nonmetallic metalloids on the left. Similarly, the transition metals occupy a region between the "virulent and violent" metals on the left side of the periodic table, and the "calm and contented" metals on the right. They effectively serve as a "transitional bridge" connecting these two regions.^[184]"

Could you please advise me if you have any concerns about any of these paragraphs? --- Sandbh (talk) 07:09, 23 October 2023 (UTC)

YBG2

"My biggest concern is related to the pairing of nonmetal classes with a “complementing” set of metals.

• The pairing of nonmetal classes and metal classes is a beautiful and symmetric, but I suspect it is a bit fringe to be so prominently displayed in this article. There are RS listed in the pictures that presumably show that a given author compared a specific nonmetal category with a specific metal category. But the sources are different for each one.

Let me draw a comparison. In Classical Planet § Alchemy we see a list of planets and corresponding metals. The entire set of pairings is well attested in RS.

But what if I only found one RS that compared the Sun to gold, a different RS that compared the moon to silver, and a third that compared Mercury to mercury, and a fourth that compared Venus to copper, a fifth, Mars to iron, a sixth, Jupiter to tin, and a sixth, Saturn to lead? In this case, I believe it would be violate WP:SYNTH to prominently display the whole set of pairings as though it were some sort of organizing principal.

The pairings of nonmetal categories with metal categories appears to be this same sort of synthesis, and so I say, no matter how beautiful and symmetrical this is, it does not belong in a WP article. I would be very interested to know what other reviewers think of this concern. YBG (talk) 06:22, 21 October 2023 (UTC)

ping Graham Beards|Michael D. Turnbull|Jo-Jo Eumerus|Double sharp|Sandbh Please consider commenting on this. I will consider this concern resolved if either (1) the nominator removes the info about complementary sets of metals, or (2) no other reviewer voices a concern about this, or (3) one other reviewer gives what they (not me) consider is a good reason that this is not a concern. YBG (talk) 13:37, 21 October 2023 (UTC)

I agree with your concern. Not only is each comparison cited to a different source, but the last one (unclassified to transition) is straightforwardly SYNTH (see ref. 158; neither source quoted actually spells out the connexion). Double sharp (talk) 14:11, 21 October 2023 (UTC)

ping Jo-Jo Eumerus|Double sharp|YBG: I've added a citation that mentions the four complementary sets. --- Sandbh (talk) 03:55, 22 October 2023 (UTC)

WP:NOT says

A Wikipedia article should not be a complete exposition of all possible details, but a summary of accepted knowledge regarding its subject. Verifiable and sourced statements should be treated with appropriate weight. (emphasis added)

Citing your own article suggests that someone as well read as you could find no other RS that organizes things this way, which seems to prove my point: this is a novel idea not yet ready for WP. I suggest that it is best to leave it out for now. In a few years, if this organizing scheme is as useful as it is beautiful, other authors will pick it up and it can be included with no objection. YBG (talk) 04:28, 22 October 2023 (UTC)

Thank you YBG.

There is nothing "novel" in this.

The background to the complementing sets is that the pairing of metals and nonmetals, and alkali metals and halogens, forms a foundational technique in chemistry education:

... we focus mainly on the gross structure – the metals are here, the non-metals are there, and so on. Once they have grasped this, you can start to show that there's some order to it. We talk about the Group 1 alkali metals and start to see that they're all similar in some way. Then at the other extreme there are the ...halogens. The idea that the table shows us how to group similar elements starts to come together in this way.

Niki Kaiser (2019)

Notre Dame High School, Norwich, UK

There is a long history in the literature of complementing sets, for example:

What, in general, is the difference between active metals, less active metals, less active non-metals, active non-metals, and inert gases…?

--- Friedenberg EZ 1946, A Technique for Developing Courses in Physical Science Adapted to the Needs of Students at the Junior College Level, University of Chicago, Chicago, p. 230

For more recent references there are:

Describe how groups of elements can be classified including highly reactive metals, less reactive metals, highly reactive nonmetals, less reactive nonmetals, and some almost completely nonreactive gases.

--- Padilla MJ, Cyr M & Miaoulis I 2005, Science explorer (Indiana Grade 6), teachers's edition, Prentice Hall, Upper Saddle River, New Jersey, p. 27

Those [elements] classified as metallic range from the highly reactive sodium and barium to the noble metals, such as gold and platinum. The nonmetals…encompass the…the aggressive, highly-oxidizing fluorine and the unreactive gases such as helium.

--- Weller et al. 2018, Inorganic Chemistry, 7th ed., Oxford University Press, Oxford, preface

A similar pattern occurs along the periods:

Across each period is a more or less steady transition from an active metal through less active metals and weakly active non- metals to highly active nonmetals and finally to an inert gas.

--- Beiser A 1968, Perspectives of modern physics, McGraw-Hill, New York

The pairing of the noble metals and gases is mentioned in no less a reputable source then Wiberg.

The pairing of the post-transition metals and the metalloids occurs even in a popular science book by Adrian Dingle (2017) who has written extensively on PT matters:

[With] no-doubt metals on the far left of the table, and no-doubt non-metals on the far right ... the gap between the two extremes is bridged first by the poor [post-transition] metals, and then by the metalloids—which, perhaps by the same token, might collectively be renamed the "poor non-metals".

That just leaves the transition metals and the unclassified nonmetals, both of which are bridging in nature, as observed by Atkins, and Welcher.

I won't fuss about this; if need be it'll be easy enough to revert the complementing sets.

That said, could you please consider the following:

• The long history of the idea of parallels among the elements between e.g. active metals, less active metals, less active nonmetals and active nonmetals.
• The cited article was published in a reliable, peer reviewed journal.
• It's been cited seven times by other authors.
• Each complementing set has been cited in other reliable sources.
• An encyclopedia, as I understand the nature of WP, collects and presents what is understood to be factual information, as is the case here.

--- Sandbh (talk) 13:08, 22 October 2023 (UTC)"

YBG

Thank you YBG.

There is nothing "novel" in this.

The background to the complementing sets is that the pairing of metals and nonmetals and alkali metals and halogens forms a foundational technique in chemistry education:

... we focus mainly on the gross structure – the metals are here, the non-metals are there, and so on. Once they have grasped this, you can start to show that there's some order to it. We talk about the Group 1 alkali metals and start to see that they're all similar in some way. Then at the other extreme there are the ...halogens. The idea that the table shows us how to group similar elements starts to come together in this way.

Niki Kaiser (2019)

Notre Dame High School, Norwich, UK

There is a long history in the literature of complementing sets, for example:

What, in general, is the difference between active metals, less active metals, less active non-metals, active non-metals, and inert gases…?

--- Friedenberg EZ 1946, A Technique for Developing Courses in Physical Science Adapted to the Needs of Students at the Junior College Level, University of Chicago, Chicago, p. 230

For more recent references there are:

Describe how groups of elements can be classified including highly reactive metals, less reactive metals, highly reactive nonmetals, less reactive nonmetals, and some almost completely nonreactive gases.

--- Padilla MJ, Cyr M & Miaoulis I 2005, Science explorer (Indiana Grade 6), teachers's edition, Prentice Hall, Upper Saddle River, New Jersey, p. 27

Those [elements] classified as metallic range from the highly reactive sodium and barium to the noble metals, such as gold and platinum. The nonmetals…encompass the…the aggressive, highly-oxidizing fluorine and the unreactive gases such as helium.

--- Weller et al. 2018, Inorganic Chemistry, 7th ed., Oxford University Press, Oxford, preface

The pairing of the noble metals and gases is mentioned in no less a reputable source then Wiberg.

The pairing of the post-transition metals and the metalloids occurs even in a popular science book by Adrian Dingle (2017) who has written extensively on such matters:

[With] no-doubt metals on the far left of the table, and no-doubt non-metals on the far right ... the gap between the two extremes is bridged first by the poor [post-transition] metals, and then by the metalloids—which, perhaps by the same token, might collectively be renamed the "poor non-metals".

That just leaves the transition metals and the unclassified nonmetals, both of which are bridging in nature, as observed by Atkins, and Welcher.

I won't fuss about this; it'll be easy enough to remove the complementing sets.

Before I do so, could you please consider the following:

• The long history of the idea of parallels among the elements between e.g. active metals, less active metals, less active nonmetals and active nonmetals.
• The cited article was published in a reliable, peer reviewed journal.
• It’s been cited seven times by other authors.
• Each complementing set has been cited in other reliable sources.
• An encyclopedia, as I understand the nature of WP, collects and presents what is understood to be factual information, as is the case here.

--- Sandbh (talk) 07:25, 22 October 2023 (UTC)

DS

Thanks Double sharp.

Some of your concerns are addressed in my 00:51, 20 October 2023 response to your philosophical concern/s.

The 7 g/cm³ figure wasn’t chosen by me. It so happened that the chart mapping the elements according to their density and EN happened to fall out that way. It was only after I drew the chart that I remembered the 7 figure.

I've changed the footnote to read:

"A survey of definitions of the term "heavy metal" reported density criteria ranging from above 3.5 g/cm³ to above 7 g/cm³.^[276]"

I feel this is a neutral statement.

I’ve shied away from 3D-electrical conductivity for the following reasons:

• Single properties don't work as per Emsley, and over two centuries of attempts have shown.
• It requires a caveat in the case of As and Sb.
• Density has a long association with pre-chemistry and chemistry, at first as a way to distinguish metals from other substances. With the isolation in 1807 and 1808 of Na and K (both being lighter than water, which was an astonishing finding in its day) chemists had to further look to chemical behaviour to conclude that Na and K were indeed metals.
• Na and K highlighted that while density was an important property often associated with metals (and it still is in terms of the loose concept of heavy metals), it wasn’t the sole determinant of their behavior i.e. there were such things as lightweight metals that still behaved chemically as electropositive metals.
• Chemistry, rather than physics so much, is the broad focus of the article.
• Electronegativity as a way to characterise the elements dates back to the days of Berzelius, in the 1810s and 1820s, with his notions of electropositive and electronegative behaviour.
• Goldwhite & Spielman (1984, p. 130) related density and EN, when they wrote, "lighter elements tend to be more electronegative than heavier ones".

Summarizing, density and electronegativity have had a significant interrelated relationship and still do.

3D electrical conductivity is nevertheless included in the table of 22 suggested single properties for distinguishing metals from nonmetals (1811–2017).

Like Metalloid, and Planet, I've attempted to broadly describe nonmetallic elements. One of the important things is the nature of their physical and chemical properties, hence the mention of density and electronegativity.

Those two properties are just two of the up to fifty or so properties that RS use in attempts to characterise nonmetals.

In light of your concerns I've changed the opening sentence to:

A nonmetal is a chemical element generally characterized by, among other properties, low density and high electronegativity (the ability of an atom in a molecule to attract electrons to itself).

This seems to be (a) accurate, with wriggle room provided by the "generally"; (b) relatively inclusive; (c) balanced; and (d) congruent with the literature.

The article further mentions a plethora of properties, and I've attempted to go to considered and considerable lengths to mention the general and indicative-only nature of those properties, including density and EN.

I’ve expanded the start of the last paragraph in the Suggested distinguishing criteria subsection to read:

Several authors^[278] have noted that, in general, and among other properties, nonmetals have low densities and high electronegativity, which is consistent with the data presented in the table.

The article mentions Sb and As being sometimes conceived of as metals:

Since metalloids occupy a transition region or "frontier territory",^[122] where metals meet nonmetals, their classification varies among authors. Some consider them distinct from both metals and nonmetals, while others classify them as nonmetals^[123] or as a sub-class of nonmetals.^[124] There are also authors who categorize certain metalloids as metals, such as arsenic and antimony, due to their similarities to heavy metals.^{[125][n 17]} In this context metalloids are here treated as nonmetals, based on their relatively low densities, high electronegativity, and chemical behavior,^[120] and for comparative purposes.^{[n 18]}

FAC response to DS

Thank you Double sharp. In my following reply, italicization appearing in quotes from the article has been added by me.

• There is no single source that I'm aware of that defines nonmetals precisely in terms of the two criteria. Rather, low density and high EN are two of the many properties mentioned in numerous texts as being characteristic of nonmetals. This is why the lede is worded the way it is namely, "A nonmetal is a chemical element generally characterized by low density and high electronegativity ...". Similary, the ◇ Definition and applicable elements ◇ section starts, "In general, a nonmetal is a chemical element that can be characterized by low density and high electronegativity." This is why the penultimate paragraph of the "Suggested distinguishing crieria" section is worded as follows:

Hein and Arena[65] observed that nonmetals generally have low densities and high electronegativity, which is consistent with the data presented in the table. Nonmetallic elements are predominantly located in the top right quadrant of this table, where density is low and electronegativity values are relatively high. In contrast, the other three quadrants are primarily occupied by metals.

The ◇ Definition and applicable elements ◇ section further caveats that, "There is no precise definition of a nonmetal;[4] any list of such is open to debate and revision.[5]"

• Nonmetals are typically characterized by physical and chemical properties. That tin has a density of 7.265 g/cm³ is, by itself, neither here nor there (so to speak). That it has an EN of 1.96 is, by itself, neither here nor there. When the two are taken together the result is an element with a relatively high density and a relatively high EN, which suggests it is not a nonmetal. I remembered that the FA Heavy metals article mentioned a range of density cut offs, one of which was 7 gm/cc: "Density criteria range from above 3.5 g/cm3 to above 7 g/cm3.[3]". The age of a source does not necessarily affect its relevance. I was going to say that I could deprecate mention of the 7 gm/cc figure to a footnote, only to find that I had already done so. I've now added a wlnk to the mention of "heavy metals" so as to place the mentioned figure into context.

Nonmetal

The variegated monatomic, diatomic and directional structures of nonmetallic elements compared to the mostly non-directional centrosymmetrical structures of metals are largely explained by differences in the number of valence electrons and atomic size. In general, whereas metals tend to have fewer valence electrons than available orbitals, the converse applies to nonmetallic elements. Consequently metals share their electrons with usually six or eight to twelve or fourteen other nearby atoms to achieve the maximum in bonding capacity. The resulting crystalline structures tend to be centro-symmetrical. In contrast, nonmetals share only as many electrons as are needed to achieve the electron configuration of the next noble gas. Nitrogen, for example, needs three electrons to achieve the electron configuration of the next noble gas, neon. It does this by sharing three of its electrons with three electrons of another atom, and in the process forms a stable diatomic nitrogen molecule in which their is a triple bond. In the case of antimony, which also needs three electrons to achieve the electron configuration of the next noble gas, its atomic size is too large to make a triple bond with another antimony atom feasible. Consequently, the crystalline structure of antimony comprises buckled layers of antimony atoms, in which each antimony atom forms a singe bond with three other nearby antimony atoms in the same sheet. Attractions between the positive nucleus of each antimony atom and the negatively charged valence electrons in other nearby antimony atoms in adjacent layers, are sufficient to further permit some minor delocalisation of electrons between layers but not to the extent of making antimony a full-blown metal. Similar considerations explain, for example, the three-dimensional network structures of silicon and germanium, in which each atom forms a single bond with four other nearby atoms, and the infinite chains comprising the crystalline structures of selenium and tellurium.

Cahn RW & Haasen P, Physical Metallurgy: Vol. 1, 4th ed., Elsevier Science, Amsterdam, ISBN 978-0-444-89875-3

DeKock RL & Gray HB 1989, Chemical Structure and Bonding, University Science Books, Mill Valley, CA, ISBN 978-0-935702-61-3

Boreskov GK 2003, Heterogeneous Catalysis, Nova Science, New York, ISBN 978-1-59033-864-3

At

YBG: Yes, At has usually been counted as a nonmetal, sometimes as a metalloid, and occasionally as a metal. Effectively, nearly all authors did not do sufficient research into the nature of At, instead classifying it as nonmetal due to its status as a halogen and the "publish or perish" imperative. The latter was way more important than diving into the nature of such a rare and highly radioactive element. Here's some more background to At as a metal, including a timeline:

The bulk properties of astatine remain unknown as a visible quantity of it would immediately self-vaporize from the heat generated by its radioactivity. It remains to be seen if, with sufficient cooling, a macroscopic quantity could be deposited as a thin film.

Qualitative and quantitative assessments of its status, including having regard to relativistic effects, have been consistent with it being a metal:

1940. Astatine was judged to be a metal when it was first synthesized. That assessment was consistent with some metallic character seen in iodine, its lighter halogen congener.

1948. Seaborg GT, "The eight new synthetic elements", American Scientist, vol. 36, no. 3, p. 368:

"They have found that it behaves in many ways like a metal and is more electropositive in character than is the case for the other halogens. This is not surprising in view of the pronounced trend in this direction as we go toward the heavier end of the halogen group, but the possible extent of this effect was apparently overlooked in the chemical searches which have been made for this element in its natural form."

1949. Bladel WJ 1947, Nuclear Chemistry: Notes on a Series of Lectures, Atomic Energy Commission, Oak Ridge, Tennessee, pp. 51–52:

"Examination of the periodic chart shows that astatine falls in the seventh group with the halogens, and hence would be expected to resemble chlorine, bromine, and iodine in its chemical behavior. In fact it was so sought by chemists for many years who missed finding it because they worked from this assumption. Actually the astatine is much more metallic than even iodine, and in this behavior it resembles that of the elements in Group VI and Group III. In Group VII, bromine, iodine, and astatine are analogous to selenium, tellurium, and polonium, of Group VI and arsenic, antimony, and bismuth of Group III. The last-named element of each of these three triads displays considerably more metallic character than do the preceding two.

Astatine is not dissolved by CCl₄ as is iodine. Its properties follow closely those of the other metals. It is precipitated as the sulfide along with bismuth, mercury, cadmium, and copper. The astatine is not volatile with iodine, can be separated by the water-CCl₄ binary extraction system, and can not be precipitated by silver ion as an astatinide. Something is known about the reduction of astatine. It can be reduced by SO₂ or zinc. Immersion of a copper plate in an astatine precipitates the astatine as a metal on the plate. This shows its ease of reduction, since copper is a quite weak reducing agent."

1950. Kleinberg J, "Unfamiliar oxidation states and their stabilization," Journal of Chemical Education, vol. 27, no. 1, p. 32:

"The behavior of astatine, in many of its reactions, is that of a typical metal; for example, hydrogen sulfide precipitates element 85 quantitatively as sulfide in hydrochloric acid solution up to 6 normal. At first glance, this is extremely surprising, but it appears less so when it is realized that iodine, the element above 85 in the family, also possesses some metallic character istics. Indeed, compounds in which iodine exists as a unipositive ion stabilized by coordination with organic amines have been prepared (7). The behavior of astatine is also in line with the increased metallic character of the elements in a given group with increasing atomic number from carbon to lead, nitrogen to bismuth, and oxygen to polonium."

1954. Fearnside K, Jones EW & Shaw EN, Applied Atomic Energy, Philosophical Library, New York, p. 102:

"The position of 85 in the periodic table is that of a halogen, yet astatine has most of the chemical properties of a metal."

1956. Encyclopædia Britannica, vol. 6, p. 823:

"Astatine may well be a metal"

1972. Batsanov calculated astatine would have a band gap of 0.7 eV [which is metalloid- and hence nonmetal-territory] (but see the 2013 entry)

1975. Furse AJ & Rendle GP, The Pattern of Chemistry, Edward Arnold, London, p. 82:

"Probably the most important difficulty would be to decide how much different astatine is from iodine, i.e. how far the trend has gone. Perhaps astatine has such a high melting point that we ought to consider the possibility that it is a metal."

1983. Edwards and Sienko speculated that, on the basis of the non-relativistic Goldhammer-Herzfeld criterion for metallicity, astatine was probably a metalloid. As the ratio is based on classical arguments it does not accommodate the finding that polonium (cf. 2006 entry following) adopts a metallic (rather than covalent) crystalline structure, on relativistic grounds. Even so it offers a first order rationalization for the occurrence of metallic character amongst the elements.

2002. Siekierski and Burgess presumed astatine would be a metal in the context of some of the properties of iodine.

2006. Restrepo et al., on the basis of a comparative study of 128 known and interpolated physiochemical, geochemical and chemical properties of 72 of the elements, reported that astatine appeared to share more in common with polonium (a metal) than it did with the established halogens and that, "At should not be considered as a halogen." In so doing they echoed the 1940 observation that, "The chemical properties of the unknown substance are very close to those of polonium."

2010. Thornton and Burdette observed that "Since elements at heavier periods often resemble their n+1 and n-1 neighbours more than their lighter congeners, eka-iodine [astatine]...was expected to be radioactive and metallic like polonium."

2013. Hermann, Hoffmann, and Ashcroft predicted At would be an fcc metal, once all relativistic effects are taken into account, and that it would have a band gap of 0.68 eV (cf. Batsanov) if only some of these effects were taken into account.

I guess I'm saying that all of the assessments of At as a nonmetal are unreliable. Hence it shows as a metal i.e., a post-transition halogen metal.

Alternatively there is always the tricolor version, which corresponds to At usually being counted as a nonmetal, sometimes as a metalloid, and occasionally as a metal. --- Sandbh (talk) 06:59, 6 October 2023 (UTC)

Uses

Uses of nonmetallic elements

Nearly all nonmetals have uses in:	Most nonmetals have uses in:	Metalloids have uses in:
Household goods, lighting and lasers, and medicine and pharmaceuticals	Agrochemicals and dyestuffs	Alloys, ceramics, oxide glasses, solar cells, and semiconductors
Some nonmetals have uses in or as: Alloys, cryogenics and refrigerants, explosives, fire retardants, fuel cells, inert air replacements, insulation, mineral acids, nuclear control rods, photography, plastics, plug-in hybrid vehicles, smart phones, solar cells, water treatment, welding gases, and vulcanization

A high-voltage circuit-breaker employing sulfur hexafluoride (SF₆) as its inert (air replacement) interrupting medium

Nonmetallic elements have distinct properties that enable a wide range of natural and technological uses. In living organisms, hydrogen, oxygen, carbon, and nitrogen serve as the foundational building blocks of life. Some key technological uses of nonmetallic elements are in lighting and lasers, medicine and pharmaceuticals, and ceramics and plastics. The accompanying table groups nonmetallic elements according to the endemicity of their uses.

The higher cost nonmetallic elements have further specific uses in, or roles as, specialized high-performance materials, structural components and electronic devices, and technological advancements and enhancements:

• Boron is used in the form of high-strength fibers for aerospace components and certain sporting goods. It is also added to steel alloys to improve hardenability.

• Black phosphorus (including as phosphorene) is employed mainly in high-performance electronic devices, including field-effect transistors (FETs), owing to its exceptional charge carrier mobility. It also has potenital applications in photodetectors, optoelectronic devices, advanced solar cells and thermoelectric materials.

• Germanium was historically used in electronics, particularly early transistors and diodes, and still has roles in specialized high-frequency electronics. It is also used in the production of infrared optical components for thermal imaging and spectroscopy.

• Xenon finds use in high-intensity discharge lamps for bright white light in automotive headlights and marine lighting. Additionally, it serves as a contrast agent in medical imaging techniques like xenon computed tomography and xenon-enhanced magnetic resonance imaging. In space exploration, xenon is a propellant for ion thrusters, known for their efficiency.

• Radon was formerly used in radiography and radiation therapy. Usually, radium in either an aqueous solution or as a porous solid was stored in a glass vessel. The radium decayed to produce radon, which was pumped off, filtered, and compressed into a small tube every few days. The tube was then sealed and removed. It was a source of gamma rays which came from bismuth-214, one of radon’s decay products. Radon has now been replaced by sources of ¹³⁷Cs, ¹⁹²Ir, and ¹⁰³Pd.

Bibliography

• Allcock HR 2020, Introduction to Materials Chemistry, 2nd ed., John Wiley & Sons, Hoboken, pp. 61—63, ISBN 978-1-119-34119-2.
• Angelo PC & Ravisankar B 2019, Introduction to Steels: Processing, Properties, and Applications, CRC Press, Boca Raton, ISBN 9781138389991
• Bajaj T, Cascella M & Borger J 2022, "Xenon", in StatPearls, StatPearls Publishing, Treasure Island, Florida, https://www.ncbi.nlm.nih.gov/books/NBK540997, PMID 31082041, viewed 4 October 2023
• Beard A, Battenberg, C & Sutker BJ 2021, "Flame retardants", in Ullmann's Encyclopedia of Industrial Chemistry, doi:10.1002/14356007.a11_123.pub2
• Bhuwalka et al. 2021, "Characterizing the changes in material use due to vehicle electrification", Environmental Science & Technology vol. 55, no. 14, doi:10.1021/acs.est.1c00970
• Bolin P 2017, "Gas-insulated substations", in McDonald JD (ed.), Electric Power Substations Engineering, 3rd, ed., CRC Press, Boca Raton, FL, ISBN 978-1-4398-5638-3
• Burke RA 2020, Hazmatology: The Science of Hazardous Materials, Vol. 3: Applied Chemistry and Physics, CRC Press, Boca Raton, p. 262, ISBN 978-1-138-31652-2
• Csele M 2016, Lasers, in Ullmann's Encyclopedia of Industrial Chemistry, doi:10.1002/14356007.a15_165.pub2
• Gaffney J & Marley N 2017, General Chemistry for Engineers, Elsevier, Amsterdam, ISBN 978-0-12-810444-6
• Gregersen E 2008, "Radon", in Encyclopedia Britannica, https://www.britannica.com/science/radon/additional-info#history, July 3, accessed 5 October 2023
• Harbison RD, Bourgeois MM & Johnson GT 2015, Hamilton and Hardy's Industrial Toxicology, 6th ed., John Wiley & Sons, Hoboken, ISBN 978-0-470-92973-5
• Imberti C & Sadler PJ, 2020, "150 years of the periodic table: New medicines and diagnostic agents", in Sadler PJ & van Eldik R 2020, Advances in Inorganic Chemistry, vol. 75, Academic Press, ISBN 978-0-12-819196-5
• Kiiski et al. 2016, "Fertilizers, 1. General", in Ullmann's Encyclopedia of Industrial Chemistry, doi:10.1002/14356007.a10_323.pub4
• King AH 2019, "Our elemental footprint", Nature Materials, vol. 18, doi:10.1038/s41563-019-0334-3
• Pawlicki T, Scanderbeg DJ & Starkschall G 2016, Hendee's Radiation Therapy Physics, 4th ed., John Wiley & Sons, Hoboken, NJ, p. 228, ISBN 978-0-470-37651-5
• Radon, Royal Society of Chemistry, viewed 3 October 2023
• Reinhardt et al. 2015, Inerting in the chemical industry, Linde, Pullach, Germany, accessed October 19 2021
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YBG and nonmetal

In general, a nonmetal is a chemical element characterized by low density and high electronegativity. They lack most or all the properties commonly associated with metals: luster or shininess; malleability and ductility; good thermal and electrical conductivity; and a tendency to produce basic oxides when combined with oxygen.

Any list of nonmetals is open to debate and revision as there is no precise definition of a nonmetal. Consequently there are variations among sources as to which elements are counted as such. The criteria applied depend on the properties viewed as most representative of nonmetallic or metallic character.

The following fourteen elements are commonly to definitively recognized as nonmetals:

Hydrogen, Nitrogen, Oxygen, Sulfur

Fluorine, Chlorine, Bromine, Iodine

Helium, Neon, Argon, Krypton, Xenon, Radon

The classification of carbon, phosphorus, and selenium is less clear cut; though commonly deemed nonmetals, some sources have labelled them as metalloids. Elements such as boron, silicon, germanium, arsenic, antimony, and tellurium, often termed metalloids, can be seen as intermediates between metals and nonmetals when clear differentiation is challenging. Nonetheless, their predominantly nonmetallic chemistry, characterized by weak acidity, also supports their classification as nonmetals.

Of the 118 known chemical elements, roughly 20% are classified as nonmetals. Astatine, the fifth halogen, is often ignored on account of its rarity and intense radioactivity; theory and experimental evidence suggest it is a metal. The superheavy elements copernicium (element 112), flerovium (114), and oganesson (118) may turn out to be nonmetals. As of August 2023 their status has not been confirmed.

Nonmetal FAC

Graham Beards

We are discussing if the article is of FA standard and I don't think it is. I also think there are problems with the title, (do chemists have a unique concept of a metal that material scientists don't share?) and current scope of the article. I find the noisy table confuses me more than it informs me. The article just doesn't come across as an "example of our best work". Sorry. Graham Beards (talk) 09:38, 24 June 2023 (UTC)

UndercoverClassicist

I don't feel in a position to support, I'm afraid. Scanning through the remainder of the article, there's still work to be done on prose, clarity and MOS. I'm not sure whether that makes me an oppose, but it certainly makes me a not yet. UndercoverClassicist (talk) 16:35, 24 May 2023 (UTC)

Nonmetal FAC intro

While the idea of what a metal is has been around since BCE times it was not until over two millenia later that the term "nonmetal" appeared. It was an unfortunate term since explaining what something isn't is quite difficult.

The main body of the article has only six sections: Definition—Properties—Types—Prevalence—Uses—History.

There is a table at the end comparing the properties of metals and the different types of nonmetals.

Since the article was last at FAC in May-June 2023, it’s been further copy edited, checked for compliance with the MOS, the title simplified, the scope honed, and the lede table streamlined.

The two prior FAC noms can be found here:

• Nonmetal (chemistry) archive 1
  
• Nonmetal archive 5

--- Sandbh (talk) 03:32, 17 September 2023 (UTC)

Notes

Article structure

To improve the flow and balance of the first two sections I've rearranged things as follows:

Before 1 Overview 1.1 Atomic structure 1.2 Electron configuration         1.2.1 The order of subshell filling 1.3 Electron configuration table 1.4 Group names and numbers 1.5 Presentation forms 2 Variations 2.1 Period 1 2.2 Group 3

After 1 Overview and variations 1.1 Group names and numbers 1.2 Presentation forms 1.3 Period 1 1.4 Group 3 2 Atomic structures of the elements 2.1 The nucleus and its surrounding electrons 2.2 Electron configurations 2.2.1 The order of subshell filling 2.3 Electron configuration table

Before, I felt there was too much technical content in the first section—which is supposed to be an overview—dealing with atomic structure and electron configurations. As well, atomic structure is important enough to merit its own section.

After, the "Overview and variations" section now has more of an holistic flavour, before moving on to look under the hood in the next section, "Atomic structures of the elements."

In the process I trimmed some duplicated content at the head of the original "Overview" section.

Nonmetal definitions

Before (what a nonmetal is not) 89 words	After (what a nonmetal is) 87 words
A nonmetal (or non-metal) is a chemical element that generally lacks a predominance of metallic properties; they range from colorless gases (like hydrogen) to shiny solids (like carbon, as graphite).	A nonmetal is a chemical element that is a poor conductor of heat and electricity, or is a mechanically weak and brittle solid the most stable oxide of which is acidic. They range from colorless gases (like hydrogen) to shiny solids (like carbon, as graphite).
They are usually poor conductors of heat and electricity, and brittle when solid, due to their electrons having low mobility.	Poor conductivity, or low structural strength when solid, occur due to the electrons in nonmetals having limited mobility.
In contrast, metals are good conductors and most are easily flattened into sheets and drawn into wires since their electrons are generally free-moving.	In contrast, metals are good conductors and most are easily flattened into sheets and drawn into wires since their electrons are generally free-moving.
Nonmetal atoms tend to attract electrons in chemical reactions and to form acidic compounds.	Nonmetal atoms tend to attract electrons in chemical reactions and to form acidic compounds.
example

WP: Chemistry

DePiep: Examining the periodic tables shown in 27 chemistry books immediately at hand to me gave the following result:

Caption text

Periodic table type	Number	Percentage
No dividing line	16	60%
Dividing line only	5	18%
Metalloids shown, no dividing line	4	15%
Dividing line & metalloids shown	2	7%

The nonmetal article says, in part:

"On a standard periodic table, they [the metalloids] occupy a diagonal area in the p-block extending from boron at the upper left to tellurium at lower right, along the dividing line between metals and nonmetals shown on some tables."

The term metalloid appears 49 times in the nonmetal article.

The phrase, "intermediate class between the metals and the nonmetals" refers to metalloids.

For the term "nonmetal halogens" here are 20 examples from the literature:

• "It will be seen that these elements of zero valence and no chemical character form a natural passage from the strongly electro-negative non-metallic halogens…"

— A review of some of the recent literature of the periodic law, RH Bradbury - Journal of the Franklin Institute, 1902

• "In the decidedly nonmetallic halogen group…"

— Qualitative analysis as a laboratory basis for the study of… Page 64, William Conger Morgan · 1906

• "And among the nonmetallic halogens we find the…"

— Recent Advances in Physical and Inorganic Chemistry - Page 245, Alfred Walter Stewart · 1920

• "In a similar manner the nonmetal halogen elements are arranged"

— Essentials of Chemistry - Page 54, Luros G · 1955

• "The alkali metals of Group la combine readily with the nonmetal halogens of Group VIIa."

— General Chemistry - Page 87, John Arrend Timm · 1966

---

• "Nitrogen was the subject of Chapter 15, and the nonmetallic halogens, of Chapter 17."

— Introduction to Chemistry - Page 226, Williams et al. · 1973

• "The electron configurations of atoms of some of the elements, the alkali metals and the nonmetallic halogens and noble gases , are given in Table 4-1."

— Geology: Our Physical Environment, Page 30, Davis et al. 1976

• "The nonmetallic halogen atoms easily pick up an electron , thus forming halide ions."

— Chemistry Decoded - Page 346, Leonard W. Fine · 1976

• "Iodine is a nonmetallic halogen , having the lowest reactivity of any substance in this group."

— Properties of Nonmetallic Fluid Elements - Volume 3, Part 2 - Page 115, Yeram Sarkis Touloukian, ‎Cho Yen Ho · 1981 · ‎p. 115

• "An activity series for the nonmetallic halogens was given in Chapter 6."

— Understanding Chemistry - Page 386, Robert J. Ouellette · 1987

---

• "Other properties are similar to those of the nonmetallic halogen elements in Group VIIA or 17 in the second column from the far right of the table…in this case, the nonmetal halogen element is reduced to its halide ion."

— Chemistry: A Basic Introduction - Pages 125, 271, George Tyler Miller · 1987

• "Iodine resembles bromine because they are nonmetallic halogens that form compounds like those of chlorine."

— Chemistry - Page 8, Nathan · 1993, p. 8

• "What causes gold to emulate many properties of the nonmetallic halogens?"

— Chemical Principles, Page 549, Steven S. Zumdahl · 1995

• "Particular but we must not forget the novel involvement of the non-metal halogens."

— The Chemistry of Evolution: The Development of our Ecosystem, R.J.P Williams, ‎J.J.R Fraústo da Silva · 2005

• "Among the other nonmetal halogens used to partially halogenate metal oxides…"

— Inorganic Reactions and Methods, The Formation of Bonds to…, A. P. Hagen · 2009, p. 221

---

• "Non-metallic halogens such as chlorine, iodine and bromine are salt-forming elements."

— "TRPM7 is regulated by halides through its kinase domain", H Yu, Z Zhang, A Lis, R Penner, A Fleig - Cellular and molecular life… 2013

• "Nonmetallic halogen element of atomic number 53…

— Hawley's Condensed Chemical Dictionary - Page 765, Michael D Larrañaga, ‎Richard J. Lewis, Sr., ‎Robert A. Lewis · 2016

• "Non-metallic halogens are very attractive"

— "Hydrothermal preparation of visible-light-driven Br-doped Bi₂WO₆ photocatalyst", P Dumrongrojthanath, A Phuruangrat, S Thongtem… Materials Letters, 2017 - Elsevier

• "…chlorine; element #17; a nonmetal halogen gas"

— Trauma, 8th Edition - Page 1139, Moore et al. 2017, p. 1139

• "…and a more detailed grouping in families of: alkali Earth, alkaline Earth, transition metal, rare Earth, other metal, metalloid, and nonmetal halogen to noble gas."

— Illustrated Encyclopedia of Applied and Engineering Physics, Robert Splinter · 2017, p. 382

“ …we focus mainly on the gross structure – the metals are here, the non-metals are there, and so on. Once they have grasped this, you can start to show that there’s some order to it. We talk about the Group 1 alkali metals and start to see that they’re all similar in some way. Then at the other extreme there are the…halogens. The idea that the table shows us how to group similar elements starts to come together in this way. ”
Niki Kaiser (2019)

---

Notre Dame High School,
Norwich, UK

Source:Unwrapping the periodic table

Smokefoot: The distinction between metals and nonmetals is a part of Chemistry 101. For example, the RSC's English Chemistry Curriculum Map for KS4 (Years 10 and 11) says, "Trends in the periodic table; Explain the reactivity and general properties as related to the atomic structure of groups 1, 7 and 0; between metals and non-metals."

When I search American Chemical Society journals for “metals” I get 287,959 hits; for “non-metals” I get 286,100 hits. Sandbh (talk) 07:52, 11 April 2023 (UTC)

Colour categories

   Alkali metal
   Alkaline earth metal
   Lanthanide
   Actinide
   Transition metal    Post-transition metal
   Metalloid
   Polyatomic nonmetal
   Diatomic nonmetal
   Noble gas

"Effectively all the literature" refers to F, Cl, Br, I, and At as halogens, indeed. They also refer to O, S, Se, Te, and Po as chalcogens (maybe some would exclude O, so let's stick to the heavy four). So why are halogens a category and not chalcogens, especially when it's common for inorganic textbooks to split their chapters by groups? The RSC table even has both, whereas the polyatomic/diatomic scheme the article you refer to recognises neither, proving once again the point that the literature is clearly not unified behind any particular categorisation scheme. What literature provides the "common sense" for the radioactives, noting that the diagonal line between metals and nonmetals meets the halogens and noble gases at At, Ts, and Og? In the literature, B and Sb are noticeably less commonly classed as metalloids than Si, Ge, As, and Te. And again, where does the name "unclassified nonmetals" come from? (talk) 15:06, 14 February 2023 (UTC)

1. In this case, halogens are a "category" and "chalcogens" are not, since two different contexts are involved. The first context is as a category for showing the metallic to nonmetallic progression across the PT e.g. from the alkali metals to the halogens, which is the traditional contrast. The second context is for naming vertical groups where both chalcogens and halogens, and others, are de rigeur. WP takes both approaches i.e. we have articles on e.g. transition metals; post-transition metals; and metalloids; and at the same time we have articles on e.g. pnictogens, and chalcogens.

2. The Wikipedia polyatomic/diatomic scheme that the Nature article used happened to be the WP scheme of the day, which the authors presumably used thinking that if it was on WP then it must've have represented some kind of consensus in the literature. In fact, the polyatomic/diatomic categories are not representative of the literature, and I now regret proposing its adoption. Older, wiser.

3. For the first context of a L-R metallic to nonmetallic transition, I feel the literature is broadly in agreement on a categorisation scheme. Perhaps the biggest and sharpest categories are alkali metals, transition metals, lanthanoids, actinoids, halogens, and noble gases. What's left? The alkaline earth metals; the metals after the transition metals; metalloids; and the rest of the nonmetals: H, C, N, O, P, S, Se.

4. My radioactives fu is not strong. I guess some of them may have have ended up where they did on account of their presence in Th and U decay chains. For Tc I know that this is an abbreviation for critical temperature. So we are talking about Tc, Rn, Ra, Po, Pm, At and Fr. We know Tc is a TM; Rn is a noble gas; Ra is an alkaline earth; Po is a metal as far as we know; Pm is an Ln; At is a halogen; and Fr is an alkali metal.

5. There is no need to lose sleep about how the period 7 elements in the p block are classified: I suggest "unknown" until enough evidence comes in to make a reasonable call.

6. According to Lists of metalloids, the % appearance frequencies are B 86, Si 95, Ge 95, As 99, Sb 87 and Te 98. The next cluster is Po 49, At 40. The gap between the first and second clusters is wide enough to conclude that the elements most commonly recognised as metalloids are those in the first cluster.

7. The term unclassified nonmetals is a descriptive version of other nonmetals.

--- Sandbh (talk) 11:37, 15 February 2023 (UTC)

Talk

Here are three reasons.

1. This chemistry stack exchange page appears to shed some light on the question:

"Q: Are the elements La and Ac considered to be in the d block or the f block of the periodic table?

A: The real lesson here is that the boundaries between "blocks" of the Periodic Table, like the boundary between "strong" and "weak" acids or bases or even between what is a stable compound and what isn't, is not sharp. Some other examples of a rough, spotty, changeable real world:

• Most simple magnesium compounds, even the best known hydride and boride compounds, are primarily ionic, but when they have covalent character the magnesium often bonds tetrahedrally as if using 3𝑝 as well as 3𝑠 valence orbitals. See for instance the coordinated structure given here for methylmagnesium chloride in THF. Beryllium shows this effect even more prominently in its wider variety of covalent compounds.

• Calcium could be called a 𝑑-block element when it bonds with its 3𝑑 orbitals in this calcium(I) compound (and yes it is +1, showing multiple oxidation states like a transition element).

• Cerium, the second element is the lantanide series, does some straddling of its own between 𝑑 and 𝑓 blocks as its valence in the metal is changeable between 3 (with a core-like 5𝑓 electron) and 4 (with this electron engaged in the bonding). See Johanssen et al. 2 and the WP article citing this reference.

• Among the actinides there is also thorium, which appears to involve only 7𝑠 and 6𝑑 valence electrons in the gas phase but brings in 5𝑓 orbitals in the metal (see this answer and the references therein)."

Johansson, Börje; Luo, Wei; Li, Sa; Ahuja, Rajeev (17 September 2014). "Cerium; Crystal structure and position in the periodic table". Scientific Reports. 4: 6398. Bibcode:2014NatSR...4E6398J. https://doi.org/10.1038/srep06398.

Krieck, Sven; Görls, Helmar; Westerhausen, Matthias (2010). "Mechanistic elucidation of the formation of the inverse Ca(I) sandwich complex [(thf)3Ca(μ-C6H3-1,3,5-Ph3)Ca(thf)3] and stability of aryl-substituted phenylcalcium xomplexes". Journal of the American Chemical Society. 132 (35): 12492–12501. https://doi.org/10.1021/ja105534w.

On a related, note Sanderson (1960, p. 8) wrote:

"If a d electron, for example, can easily behave like an f electron, or vice versa, the argument as to the exact ground state configuration becomes relatively unimportant."

That is to say, both La and Lu can relatively easily behave as if they were f elements never mind their 4f⁰5d¹6s² and 4f¹⁴5d¹6s² formal configs.

Sanderson RT 1960, Chemical Periodicity, Reinhold, New York

The chemistry stack exchange response and Sanderson show that the presence of this or that kind of electron, especially in marginal cases at the borders of putative blocks is less than a major consideration.

2. Each of the two options has something to offer and each comes with advantages and drawbacks.

For the La-Ac form, many of the advantages were set out in my article that appeared in Foundations of Chemistry (13 citations). As well, each block starts with the first appearance of the relevant electron.

For the disadvantages, I suppose the biggest is that it requires a split d-block, if shown in 32-column form.^ And Sc-Y-La-Ac messes up the regularity of spin multiplicity.

^ I qualify this by noting that a split between groups 1 to 3 and 4 accords with a transition from largely ionic chemistry to covalent chemistry.

For the Lu-Lr form, some advantages I can think of are:

• if the 4f row is shown as La to Yb, the number of f electrons in each atom corresponds to its position in the row, in all bar three cases (La, Ce and Gd);
• the situation in the 5f row is a little more involved, but still pretty regular;^^
• a cohesive d-block in the 32-column form;
• more amenable (?) to being mathematised.

^^ For Ac–No, the actinide series can be divided into three relatively cohesive sets:

• Ac and Th, which each have a number of d electrons equal to their position;
• U and Am, which have a mix of d and f electrons; and
• Pu to No, in which the number of f electrons in each atom corresponds to its position in the row in all bar one case (Cm).

Some drawbacks are:

• an extra differentiating electron discrepancy;
• Sc-Y-Lu-Ac is inconsistent with stoichiometric considerations;
• reduced regularity of term symbols;
• disaggregated lanthanide contraction.

3. Over the past 85 years, since it was found that La and Lu each had a d differentiating electron and (ostensibly) an equal claim to the position under Y in group 3, nobody has been able to mount a sufficiently compelling case for the superiority of either Sc-Y-La-Ac or Sc-Y-Lu-Lr over the other. In the category of "insufficiently compelling" I include "making such a decision on the basis of convention".

DS

1. The abstract of the Chinese paper says:

"The Ln 4f orbitals do not directly participate in bonding from the view-point of traditional bonding theory..."

OK; that's interesting.

"...but may influence the bonding to a certain extent through mixing a little match orbitals into the localized 4f orbitals and mixing some 4f component into the delocalized molecular orbitals, causing the bond lengths shortened and the bonding energy increased by about several hundredths in general."

OK; so we are talking about several per cent.

On page 1380 (right column) they say there is almost [bold added] no difference for Lu vis à vis f participation, i.e. there is some f participation.

Now, Table 1 shows that the difference in calculated bond lengths for frozen 4f v unfrozen 4f is CeS 0.011; EuS 0.005; GdS 0.003; YbS 0.002; LuS 0.001. Table 2 shows that the difference in calculated bond energies for frozen 4f v unfrozen 4f in CeO is 2.42 (eV); EuO 1.06; GdO 1.03; YbO 0.58; Lu 0.07 (i.e. 7%).

So there is some 4f involvement in the Lu compounds.

Table 3 shows that 4f contribution to the bond level for frozen and unfrozen 4f is CeO 0.065:0.065; EuO 0.017:0.033; GdO 0.012:0.045; YbO 0.008:0.008; Lu 0.007:0.007.

Either way, Lu has some 4f contribution.

In the conclusion the authors write: "In Lu compounds 4f orbitals basically [bold added] have no contribution to bond formation." That is to say, they did not write, "In Lu compounds 4f orbitals have no contribution to bond formation" because they couldn't.

2. I didn't write that "f is the most significant orbital for Lu."

Instead, here's what I wrote:

"As to Sc and Y as f-elements my position is (as set out in my peer-reviewed article in FoC) that it is the most important orbital that influences the positioning of an element. Hence La is d-block and Lu is f-block given La is not subject to the f-induced Ln contraction whereas Lu is."

For La, the most important orbital is d. For Lu, the most important orbitals are f (the poor shielding of which results in the Ln contraction) and d.

3. That La fits better under Y than Lu on e.g. stoichiometric grounds, per Restrepo, does not strike me as a side issue. It certainly wasn't for DIM. Simon Cotton and team's recent article noting zero support for shifting Lu under Y is the same.

I further wrote in my article:

”For example, since yttrium is commonly found in nature together with the heavier lanthanoids including lutetium it is sometimes argued that this supports Group 3 as Sc-Y-Lu-Ac (Thyssen and Binnemans 2011, p. 80). In fact yttrium is unique among the rare earth elements in that, depending on the circumstances, it can behave like a light lanthanoid e.g. Pr, Nd, Sm, or a heavy lanthanoid e.g. Dy, Tm, Lu (Marsh 1947, p. 1084; Jowsey et al. 1958, p. 64; Bünzli and McGill 2011, pp. 19, 26; Gupta and Krishnamurthy 2005, p. 165). In terms of the stoichiometry of binary compounds, yttrium is reported to be more like lanthanum than lutetium (Restrepo (2018, pp. 94–95). In a similar vein, lanthanum has a sufficiently distinct nature compared to the cerium to lutetium series (Liu et al. 2019).”

4. I acknowledged La 4f involvement in my FOC article (note 29). That said, this is not of the same magnitude as occurs in Ce to Lu, by way of the Ln contraction, which starts at Ce and peaks at Lu.

5f is present in Th metal, and explains its crystalline structure.

5. The ionic v covalent distinction is a useful rubric in chemistry, as relied on by the several authors cited in my peer-reviewed article. As expressed by Nelson (2011):

"…care needs to be taken to remember that…[this classification scheme] is only an approximation, and can only be used as a rough guide to the properties of the elements. Provided that this is done, however, it constitutes a very useful classification, and although purists often despise it because of its approximate nature, the fact is that practising chemists make a great deal of use of it, if only subconsciously, in thinking of the chemistry of different elements.

While Nelson was referring to a scheme for classifying the nonmetals according to their electronegativity, the principle is the same.

5a. Li is over H on account of a mix of historical, didactic, pragmatic, electronic and physicochemical considerations.

Yes, different physicochemical properties suggest different answers to the group 3 puzzle. Hence there are other considerations, including electron configurations.

If the PT was truly electronic then Scerri and Parson’s argument…

"For the purpose of selecting an optimal periodic table we prefer to consider block membership as a global property in which we focus on the predominant differentiating electron.” (Scerri and Parsons 2018, p. 151)

…supports La in group 3, since such a table has one less differentiating electron discrepancy than an Lu table.

6. I did not say:

"blocks aren't specifically an electronic concept."

Instead, what I wrote was:

"Blocks are indeed named by subshells but that does not limit their scope to electronic phenomena."

I had in mind what Philip Stewart wrote:

"The division into blocks is justified by their distinctive nature: s is characterized, except in H and He, by highly electropositive metals; p by a range of very distinctive metals and non-metals, many of them essential to life; d by metals with multiple oxidation states; f by metals so similar that their separation is problematic. Useful statements about the elements can be made on the basis of the block they belong to and their position in it, for example highest oxidation state, density, melting point… Electronegativity is rather systematically distributed across and between blocks."

7. Re: "different physicochemical properties suggest different answers to the group 3 puzzle." Not so. Based on the smoothness of 40 physicochemical trendlines, La is a better option by 6.0%. That said, it is evident that the PT is based on more than physicochemical considerations.

7a. QM is one more of the considerations that go into compiling the PT.

8. Spectroscopy is another of the considerations that go into compiling the PT. I will grant you that La-Ac under Lu-Lr brings out a nice secondary relationship. That said, a periodic table cannot show all desirable relationships. Further, it is rather easy to maintain the secondary relationship in an La table. So, group 3 becomes 3* and another 3* is placed over Lu-Lr. The asterisk note then reads: "Group 3 bifurcates after Y into an -La-Ac tranche and an -Lu-Lr tranche.

Group 3 poll wording

Question

Based on the considerations listed below (ca. 450 words) should the default periodic table in the lede of the periodic table article, show group 3 as Sc-Y-La-Ac? It currently shows Group 3 as Sc-Y-Lu-Lr.

An IUPAC-commissioned survey of university textbooks on how group 3 of the periodic table is shown. See: Progress tab, Dec 2019 update, here.

Considerations
1. IUPAC has not recommended any form of PT.

2. Whether group 3 should be [A] Sc-Y-La-Ac or [B] Sc-Y-Lu-Lr has been debated since at least 1921; both variations occur in the literature.

3. A 1988 IUPAC report on the 1-18 group numbering scheme briefly mentioned the composition of group 3. It said the group should be Sc-Y-Lu-Lr, citing several sources in favour but not citing any sources supporting Sc-Y-La-Ac. In the event, the next edition of the IUPAC Red Book showed the 18-column Sc-Y-*-** form on its inside cover and, in the appendix, 8- and 18-column Sc-Y-*-** forms and a 32-column Sc-Y-Lu-Lr form.

4. As students and instructors are typically puzzled by this variation, IUPAC started a project in 2015 to give a recommendation to IUPAC on whether group 3 should be [A] or [B].

5. A 2021 provisional progress report by the project found there was no objective way of adjudicating in favour of either [A] or [B]. It added it was therefore important IUPAC make a recommendation, which in the final analysis is one of convention rather than decided on objective scientific grounds. The report added:

Perhaps a compromise could be reached on "[B]", on the basis of three desiderata. First, it displays all the elements in order of increasing atomic number. Secondly, it avoids splitting the d-block into two highly uneven portions, and thirdly, it depicts all the blocks of the periodic table in accordance with the underlying quantum mechanical account of the periodic table which calls for 2, 6, 10 and 14 orbitals to occur in the extra-nuclear electron-shells.

6. As part of their work the project team surveyed PTs in university textbooks from the 1970s to the 2010s. Version [A], Sc-Y-La-Ac, was most common in each decade (see accompanying chart), but in the 2010s it was a plurality not a majority.

7. In a public address to the University of Hampshire on March 1, 2022, Scerri said [at ca. 54:11]:

"...i'm afraid that we this [Group 3 question] has not been resolved it's been left hanging and i'm afraid it's i this is just a personal opinion which i hesitate to say publicly but i think they're they're copping out iupac is afraid of a pluto situation or something like it where a major change to the periodic table occurs and everybody freaks out and says no no you've destroyed my favorite periodic table."

8. Relevant WP policy includes WP:ENC, WP:NPOV, WP:DUE.

Conflict of interest declarations:

• Eric Scerri, chair of the IUPAC group 3 project, has written extensively in support of Sc-Y-Lu-Lr.
• Sandbh, the originator of this RFC, has written in support of Sc-Y-La-Ac.

Votes

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Group 3 poll wording (mini)

Question

Based on the considerations listed below should the default periodic table in the lede of the periodic table article be changed to show Group 3 as Sc-Y-La-Ac? It currently shows Group 3 as Sc-Y-Lu-Lr.

An IUPAC-commissioned survey of university textbooks on how group 3 of the periodic table is shown. See: Progress tab, Dec 2019 update, here.

Please reply Yes or No with a brief supporting statement in the Survey. Do not respond to other editors in the Survey. The Discussion section is for back-and-forth discussion.

Considerations
1. A 2021 provisional progress report  by an IUPAC Group 3 project team found there was no objective way of adjudicating in favour of either Sc-Y-La-Ac or Sc-Y-Lu-Lr.

2. The project team surveyed periodic tables in university textbooks from the 1970s to the 2010s. Sc-Y-La-Ac was most common in each decade (per the chart), but in the 2010s it was a plurality not a majority. In this light the current default periodic table in the lede of the periodic table article is not representative of the literature.

3. The project team suggested that perhaps group 3 could be shown as Sc-Y-Lu-Lr. They did so since, compared to Sc-Y-La-Ac, this would avoid a split d-block if the table was shown in 32-column form. The form with 32-columns appeared in five of the 193 university textbooks surveyed.

4. Advice from the editor of IUPAC’s Chemistry International is as follows:

I have consulted with Division II former officers who have in length followed the project which ultimately only ended with a provisional report. As it happened, the task group could not provide a way forward to the project, and the ongoing debate is an ample illustration of that. In consequence, the Inorganic Chemistry Division is for now considering the matter closed. (F Meyers pers. comm., May 5, 2023)

The mention of an “ongoing debate” is a reference to Neve (2022), who wrote: "Evidence of [a] cold reception of the IUPAC panel working hypothesis is already manifest in the work of several scholars."

5. Relevant WP policy includes WP:ENC, WP:NPOV, WP:DUE.

Interested parties

• Eric Scerri, chair of the IUPAC Group 3 project team, has written extensively in support of Sc-Y-Lu-Lr
• Sandbh, sponsor of this RfC is the author of a peer-reviewed journal article in support of Sc-Y-La-Ac

Survey

Discussion

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NM article CE

Before

Definition and applicable elements
A nonmetal is a chemical element that has low density and moderate to high electronegativity. They also lack metallic attributes such as luster, deformability, good thermal and electrical conductivity, and low electronegativity.[11] Since there is no rigorous definition of a nonmetal,[10][12][13] some variation exists among sources as to which elements are classified as such. The decisions involved depend on which property or properties are regarded as most indicative of nonmetallic or metallic character.[14]

After

Definition and applicable elements
Properties characterising nonmetals include low density[00] and moderate to high electronegativity[00] (the power of an atom to attract an electron to itself). Some also lack metallic attributes such as luster, deformability, and good thermal and electrical conductivity.[11]

There is is no rigorous definition of a nonmetal; [10][12][13] some variation therefore exists among sources as to which elements are classified as such. The decisions involved depend on which properties are regarded as most indicative of nonmetallic character.[14] Such properties include low density, low deformability, moderate to high electronegativity (the power of an atom to attract an electron to itself) and, for those nonmetals that combine with oxygen, acidic oxides.

Since there is no rigorous definition of a nonmetal,[10][12][13]

Shiny: B, C, Si, P, Ge, As, Se, Sb, Te, I (10)
Coloured: F, S, Cl, Br (4)
Colourless: H, He, N, O, Ne, Ar, Kr, Xe, Rn (9)

Line 35

Before:
In chemistry, a nonmetal is a chemical element that generally lacks a predominance of metallic properties...

After:
A nonmetal is a chemical element that lacks a predominance of metallic properties...

I think that exclusion of In chemistry, a works only if the name of the article becomes "Nonmetal (chemical element)". I included the generally qualifier to indicate that this was a qualitative judgement.

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Before:
Nearly all nonmetals have individual uses in medicine and pharmaceuticals; lighting and lasers; and household items.

After:
Nearly all nonmetals have uses in medicine and pharmaceuticals; lighting and lasers; and household items.

I included "individual" as not all nonmetals have uses in all three areas.

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Before:
Some elements have a marked mixture of metallic and nonmetallic properties;

After:
Some elements have a mixture of metallic and nonmetallic properties;

Virtually all elements, to varying degrees, have a mixture of metallic and nonmetallic properties. Only a few have such a mixture to a marked extent.

Line 48

Before:
A nonmetal is a chemical element that has, among other properties, a relatively low density and moderate to high electronegativity. More generally, they lack a preponderance of more metallic attributes such as luster, deformability, good thermal and electrical conductivity, and low electronegativity.

After:
No widely accepted specific definition of a nonmetal exists. Properties characterising nonmetals include low density, low to moderate electronegativity, being brittle if solid, and

a chemical element that has low density and moderate to high electronegativity. They also lack metallic attributes such as luster, deformability, good thermal and electrical conductivity, and low electronegativity.

Tricky. The "after" version does not quite work, since quite a few nonmetals have luster (e.g. C, black P, Se and I) and C, As, Sb are pretty good electrical and thermal conductors.

Before:
Fourteen effectively always recognized as such are hydrogen, oxygen, nitrogen, and sulfur; the corrosive halogens fluorine, chlorine, bromine, and iodine; and the noble gases helium, neon, argon, krypton, xenon, and radon (see e.g. Larrañaga et al).

After:
Fourteen almost always recognized are hydrogen, oxygen, nitrogen, and sulfur; the reactive halogens fluorine, chlorine, bromine, and iodine; and the noble gases helium, neon, argon, krypton, xenon, and radon (see e.g. Larrañaga et al)

Suggest replacing "reactive" with "highly reactive" (in order to distinguish them from H, O, N and S. Sandbh (talk) 02:33, 3 October 2022 (UTC)

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Line 86

Before:
Outwardly, about half of nonmetallic elements are colored or colorless gases; most of the rest are shiny solids. Bromine, the only liquid, is so volatile that it is usually topped by a layer of its fumes; sulfur is the only colored solid nonmetal.

After:
About half of nonmetallic elements are gases; most of the rest are shiny solids. Bromine, the only liquid, is so volatile that it is usually topped by a layer of its fumes; sulfur is the only colored solid nonmetal.

Suggest this ce be reverted given the reference to S as being colored. Sandbh (talk) 02:46, 3 October 2022 (UTC)

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NM article

A noble metal is ordinarily regarded as a metallic chemical element that is more or less reluctant to combine with oxygen and usually found in nature in a raw form. Gold, platinum, and the other platinum group metals (ruthenium, rhodium, palladium, osmium, iridium) are most often so classified. Silver, copper and mercury are less often to sometimes included as noble metals although each of these usually occurs in nature combined with sulfur.

The number of elements counted as noble metals can be smaller or still larger in more specialized fields of study and applications. In physics, there are only three noble metals: copper, silver and gold. In dentistry, silver is not always counted as a noble metal since it is subject to corrosion when present in the mouth. In chemistry, the term noble metal is sometimes applied more loosely to any metallic or semimetallic element that does not react with a weak acid and give off hydrogen gas in the process. This broader set includes copper, mercury, technetium, rhenium, arsenic, antimony, bismuth and polonium, as well as gold, the six platinum group metals, and silver.

NM comments

Thanks for the comments.

My general point is that Wikipedia editors sometimes seem to focus on defining terms with the implication that practioners follow those definitions, when in fact practitioners rarely fuss about such definitions.

The disconnect arises because few editors are practitioners but implicitly purport to speak for them.

No harm done I guess, except that definitions are just definitions: definitions are no substitute for facts, and the exposition of facts is supposed to be the main job of editors.

Of the tens of thousand of publications appearing annually, no doubt the term noble metal occurs often.

To which I say, so what?

My specific point is that noble metal is about metals (bands, corrosion, heterogeneous catalysis), but nobility is irrelevant to compounds and ions.--Smokefoot (talk) 13:54, 16 April 2022 (UTC)--Smokefoot (talk) 13:54, 16 April 2022 (UTC)

Smokefoot, You gave me a lot to think about, thanks.

I can't speak for other editors and a possible disconnect between definitions and practice. OTOH, MOS:FIRST suggests that the first sentence of the lead should tell the nonspecialist reader what the subject is, be in plain English and, if the subject is definable, then the first sentence should give a concise definition. Since the term "noble metals" is ill-defined, the best that can be done is to survey the literature and sketch a defintion on that basis. The facts will vary depending on the source, and judgements will need to made about which facts to include and any differences between sources. Since chemistry is replete with fuzzy definitions the result ought to be par for the course.

The "so what" of noble metals, as I see it, is to wonder what is so special about them that merits categorising them as such.

I kind of get your distinction between metals, and compounds and ions, in that we do not speak of noble compounds or noble ions. And few chemists work with pure elements, so I can see that the notion of "noble metals" wouldn't be immediately relevant. OTOH, noble metals form solvated aqueous ions, and Schweitzer and Porterfied (2010), in The Aqueous Chemistry of the Elements, discuss Ru, Rh, Pd, Os, Ir and Pt together under the rubric, "Introduction to the Noble Metal Elements". Rayner-Canham (2018), in "Organising the transition metals", assigns the PGM + Au to a cluster, on the basis of their behaviour under oxidizing conditions: doi:10.1093/oso/9780190668532.003.0013. Much has been written about the analytical chemistry of noble metals. This all strikes me as "chemistry" over and above the metals by themselves, at least as far as their behaviour in ionic form is concerned. For the compounds, at least the noble metals are more of less characterized by the unstable nature of their oxides, which have a reputation for decomposing when heated.

Brooks (1992, p. 9), in Noble metals and biological systems: their role in medicine, mineral exploration, and the environment, adds that:

"The most noteworthy feature of compound formation in the noble metals is their ability to form complexes. It is these complexes that determine their abundance and transport within the biosphere, and it is these complexes that govern the development and use of noble metal drugs in medicine."

(Obviously, complex formation is not limited to noble metals but it is evidently the combination of properties of the noble metals that make them distinctive.)

Double sharp, yes, the category of noble metals is similar to attempting to distinguish between metals and nonmetals. There is universal agreement that Au is a noble metal, just like there is universal agreement that Cs is a metal and F is a nonmetal. From there, Au and Pt are universally regarded as noble metals in chemistry whereas Cu-Ag-Au are counted as the noble metals in physics. After that, the broadest definition of what is a noble metal extends to the other ten metals having a positive standard reduction potential: Tc, Re, the other 5 PGM; Hg, Bi, Po. And then there are As and Sb which are among the elements commonly recognised as metalloids. That said, the other five PGM and Hg are the only ones I've seen being unambiguously counted in the literature as noble metals.

The answer to my original physics-based question appears to lie in three sources:

1. A Physics Stack Exchange Q&A (2019) on "Role of 𝑑 -band in metals";
2. a Nature article (1995) on "Why gold is the noblest of all the metals", and
3. a ChemPhysChem article (2020), "Chemical causes of metal nobleness".

Some of the physics invoked in these sources is beyond by my ken so feel free to point out my errors, in the following interpretations.

Source 1 says that d states have less spatial extent than s- or -states, and that in transition metals the more localized outer 3d-, 4d- and 5-d states screen the interaction of the half-filled outer s-band with other states. So, early TM supposedly react more readily with e.g. O than later TM. This screening is most efficient if the outer d-shell is completely filled as in Cu-Ag-Au. While I don't understand everything written in this source I've hopefully understood the gist of it.

Source 2 says in its abstract:

"Gold is the least reactive metal towards atoms or molecules at the interface with a gas or a liquid. The inertness of gold does not reflect a general inability to form chemical bonds, however—gold forms very stable alloys with many other metals. To understand the nobleness of gold, we have studied a simple surface reaction, the dissociation of H₂ on the surface of gold and of three other metals (copper, nickel and platinum) that lie close to it in the periodic table. We present self-consistent density-functional calculations of the activation barriers and chemisorption energies which clearly illustrate that nobleness is related to two factors: the degree of filling of the antibonding states on adsorption, and the degree of orbital overlap with the adsorbate. These two factors, which determine both the strength of the adsorbate-metal interaction and the energy barrier for dissociation, operate together to the maxima] detriment of adsorbate binding and subsequent reactivity on gold."

This is consistent with what Source 1 said in the following passage:

"In the case of Cu, Ag, and Au, the screening effect is particularly strong, because the upper 𝑑-bandedge lies energetically deep below the Fermi-level (due to complete 𝑑-band filling as explained above), and thus corresponding anti-bonding states in the vicinity of this edge are (generally) more or less completely filled leading to a strong suppression of interaction with the reactant."

Source 3 is remarkably comprehensive. Here's the abstract:

"Humans have appreciated the 'noble' metals for millennia, yet modern chemistry still struggles with different definitions. Here, metal nobleness is analyzed using thermochemical cycles including the different bulk, gas, and solution states implied by these definitions. The analysis suggests that metal nobleness mainly reflects inability to fulfil the electron demands of electronegative oxygen. Accordingly, gold is the most noble metal in existence, not because of d-band properties of the solid state, but because gold’s electronegativity is closest to that of oxygen, producing weaker polar covalent bonding. The high electronegativity arises from the effective nuclear charge due to diffuse d-states, enforced by relativistic effects. This explanation accounts for the activity series, corrosion tendency, and trends in oxygen chemisorption, which other models do not. While gold is the most noble metal, the ranking of Ag, Pt, and Pd depends on the thermochemistry as discussed in detail.

Here's what I noticed in this article:

• In the abstract, I don't understand the reference to "diffuse" d-states (but I return to this later on).
• "These [noble] metals are less reactive towards oxygen, the major oxidant of this planet’s atmosphere, and are less willing to give away their electrons in solution, otherwise a hallmark of metals, as measured by their high standard half reduction potentials." (p. 3)

The reference to oxygen as the major oxidant of Earth may explain why the corrosion of Ag by S is overlooked in some cases whereas in a few other occasions its noble status is queried.

• "...the relative nobleness of metals depends substantially on the reactivity considered and the theory applied... [italics added]" (p. 3)
• "Surprisingly, whereas single [italics added] theories have been applied to rationalize metal nobleness in several cases, a combined perspective and analysis of the most important features that define nobleness seems missing in the literature." (p. 3)

In classification science, classes are usually classified by more than two criteria.

• "[This] analysis is particularly aided by thermochemical cycles that feature both the solid bulk metal state, the metal atoms in gas phase, and the aqueous solvated metal ions. Much of the confusion relates to the fact that the defining processes do not always involve the same of these states. For example, the "physicist" definition of nobleness focuses on the properties of the d-band and orbital overlap of the bulk metal interacting with an adsorbed atom^{[source 2]}, whereas the "chemist" definition focuses mainly on the solution electrochemistry." (p. 3)
• "From the analysis, it emerges that nobleness is not primarily caused by the d-band structure [italics added] of the bulk metals but to the state-independent and thus more universally applicable electronegativity of the metal atoms... Since the descriptor applies to all thermodynamic states, which e.g. d-band properties do not, it lends promise to estimates of metal reactivity and nobleness in systems without band structure, e.g. single-atom catalysts, solvated ions, clusters, and superatoms of much interest in current research efforts.^[20–24]" (pp. 3–4)

At this point I thought, "Far out! Really?" Mere EN is the primary cause of nobility in metal atoms?

Table 1 in the article (p. 5) then ranks the nobleness of Ni, Pd, Pt, Cu, Ag, Au, and Hg according to 12 descriptors/properties relevant to understanding nobility.

• the standard half reduction potential of the divalent metal ion, E° (M²⁺ + 2e^– → M)
• the reactivity towards pure strong acids HCl and HNO₃
• the experimental and computed enthalpy of chemisorption of O2 to the bulk metal surface
• the d-band center energy of the solid metal
• the first ionization potential and electron affinity of the gas-phase metal atom
• the Pauling electronegativity
• the bulk polycrystalline metal work function
• the relativistic s-shell contraction and oxophilicity of the metal; and
• the cohesive free energy (free energy of atomization) of the bulk metal state.

These 12 properties are then discussed,

• "The values of the listed properties are not necessarily exceptional to the noble metals. For example, the first IP of the group-12 metals mercury (10.4 eV) and zinc (9.4 eV) are higher than that of gold (9.2 eV) due to their complete s- and d-shells." (p. 5)
• "The common view that gold is the most noble metal is directly rationalized by gold having the highest rank when averaged over the properties in Table 1 typically associated with nobleness. It is this consensus, rather than any single property alone, [italics added] which explains the universal acceptance of gold as the most noble metal." (pp. 4–5)
• "In contrast, the second place is fiercely contested. Specifically, the relative ranking of Pt, Pd, and Ag is a matter of substantial interest and disagreement: Thus, it has been argued that the completely filled d-shell makes the coinage metal Cu (and by inference Ag) more noble than Pt and Pd^[19], and DFT-computed O2-chemisorption enthalpies put all coinage metals before platinum^[29], yet, no other property of Table 1 supports the notion that Cu is noble. Electrochemical^[27] and corrosion data^[40,41] and electronic properties suggest that Pt and Pd are particularly noble." (p. 6)

In fact the average rankings across the 12 properties are: Au 1.5; Pt 2.58; Ag 3.0; Pd 3.75; Hg 4.8; Cu 5.08; Ni 5.5, so there is no contest for second place: Pt is the winner.

• "As discussed further below, the electrochemical definition involves two specific states of the metal, the bulk solid state and the hydrated metal ion state." (p. 7)
• "Resistance toward strong acids is part of the chemist’s typical definition of nobleness...Aqua regia, the famed mixture of HCl and HNO3, solvates gold but not silver, whereas HNO₃ can dissolve silver but not gold, i.e. the reactivity depends on both the metal and acid as a pair." (pp. 7–8)
• "A useful definition of nobleness is the negative heat of chemisorption (ΔHchem) of molecules to the bulk metal surface. A more exothermic chemisorption implies that the metal surface binds more strongly to the adsorbed atom, which again implies higher reactivity. A previous attempt to explain nobleness^[19] used H₂ chemisorption as defining reaction. A more logical choice is chemisorption of O₂, because... it is the atmospheric oxygen responsible for the corrosion that has inspired the concept of noble metals for thousands of years much more than reactions with H₂." (pp. 9–10)
• "Without relativistic effects, Ag can appear the noblest of all metals, perhaps explaining its absence in the previous study^[19]. Later more complete computations^[30], tabulated in Table 1, confirm this, i.e. that the non-relativistic d-band center is lower for Ag than for Au, clearly not explaining why gold is more noble than silver. Finally, Cu was found to be much more noble than Pt and was referred to as a “noble metal” together with Au^{[Source 2]}. These points should not be taken as a criticism of the d-band center^[55], which remains a useful descriptor in particular if corrected for relativistic spin-orbit effects^[53] and structural and charge perturbations on the metal surface^[56]. Hg, Cd, and Zn have lower d-band centers, so one needs to invoke the antibonding states of the adsorbing molecule, and neglect of spin-orbit coupling makes the d-band inherently more uncertain than the experimental descriptors in Table 1. In conclusion, both the d-band center and the total number of valence d-electrons correlate decently with the empirical tendency of nobleness, as also summarized in Table 1." (p. 12)
• "The most important fundamental variation in the d-transition series is the increased effective nuclear charge moving towards the right, which arises from the gradual occupation of spatially diffuse d orbitals. This effective charge stabilizes the valence electrons of the late transition metals, which makes them less reactive towards electronegative elements such as oxygen, which requires a partial electron transfer from the d-band to the electronegative adsorbate atom." (p. 12)

It seems that the reference to spatially diffuse d orbitals is referring to the relatively poor shielding capacity of the d electrons.

• "The nobleness of Pt and Au is significantly enhanced by relativistic effects." (p. 13)
• "The noble metals are among the least oxophilic, or most “thiophilic”, in the periodic table^[38], although even these metals can be oxidized under aggressive conditions such as ultraviolet light and ozone^[65]. Accordingly, they are less reactive towards oxygen and favor sulfur and other less electronegative adsorbing atoms in competition with oxygen, as is well-reflected in their most prominent mineral ores." (p. 15)
• "The noble metals generally tend to adopt cubic closest packed structures, which is probably not a coincidence but relates to the same underlying cause, the high effective nuclear charges producing small metal radii in these metals. A good negative control of this hypothesis is supported by the group 12 metals with larger radii (Zn, Cd, Hg) adopting hexagonal or other structures. The major drivers of nobleness, as explained above, are ultimately, after account of the sizable relativistic effects on the 5d/6s states, the effective nuclear charge and the resulting electronegativity, which should be considered in context with the adsorbate atom’s electronegativity to estimate the strength of the adsorption." (p. 22)

The crystalline structures of the TM are:

Sc  Ti  V   Cr  Mn  Fe  Co  Ni  Cu  Zn
HCP HCP BCC BCC αMn BCC HCP FCC FCC HCP
---------------------------------------
Y   Zr  Nb  Mo  Tc  Ru  Rh  Pd  Ag  Cd
HCP HCP BCC BCC HCP HCP FCC FCC FCC HCP
---------------------------------------
La  Hf  Ta  W   Re  Os  Ir  Pt  Au  Hg
αLa HCP BCC BCC HCP HCP FCC FCC FCC Rho

• "Because electronegativity is a major driver of metal nobleness and reactivity, it also partly explains why noble metals are very proficient at forming alloys with metals that differ from them, notably d-transition metals." (p. 24)
• "The d-band is not the reason for nobleness but only a modestly correlating feature. This finding is important because research increasingly addresses nano-sized systems and clusters and even single-atom catalytic systems where d-band considerations are inappropriate^[20,22,77]." (p. 25)
  

Conclusions

• I think I have enough now to be able to provide a simple explanation of the physics-based notion of a noble metal and how a complete set of 10 electrons contributes to nobility.
• Source 3 provides an almost solid outline of what noble metals are:

"In the periodic table, metals to the lower right of the d-transition series such as gold, platinum, silver, and palladium are the most noble according to human experience. These metals are less reactive towards oxygen, the major oxidant of this planet’s atmosphere, and are less willing to give away their electrons in solution, otherwise a hallmark of metals, as measured by their high standard half reduction potentials. Humans have appreciated them for thousands of years due to their rarity, malleability, and exceptional resistance to corrosion, making them ideal stores of value and coinage metals."

• But this isn't quite right since Os is unworkably hard and brittle even at high temperature.
• I'm especially impressed by the 12 properties or diverging definitions of nobleness used to understand nobleness.
• I'd earlier wondered about W and its EN of 2.36 and what bearing this had on the nobility question. There's evidently more to W than its high EN. When I looked up the values for its other 11 properties, and worked out where its average place was compared to Au 1.5; Pt 2.58; Ag 3.0; Pd 3.75; Hg 4.8; Cu 5.08; and Ni 5.5, I got a figure of about > 4.83 i.e. maybe in the vicinity of Hg and Cu, which seems like an OK outcome. W doesn't occur in native form whereas Hg can rarely be found as the pure metal in droplets trapped in rocks. W too, is quite oxophilic. On a normalised scale of oxophilicity (low = 0; 1 = high) W has a rating of 0.8 compared to 0.0 to 0.4 for the PGM, Au and Ag: doi:10.1021/acs.inorgchem.6b01702, p. 9463.

PR2

Modern uni-level chemistry textbooks vary at the margins on which elements are counted as nonmetals. It comes down to the perspective of interest of the author—as noted in the article—or, more often, which older reference they decided to base their decision in the face of publish or perish. The situation hasn't changed since the 1950s–early 60s, when interest in the semiconducting properties of first germanium, and later silicon, took off.

Most scholarly monographs on nonmetals (or metalloids) appeared from 1966 to 1977. Steudel (1977) published a 2nd ed. in 2020 ($US90, or ca. $117 for the e-book!) which contains no new encyclopedia-level information about nonmetals. A fair summary of modern thinking as to which elements are nonmetals inextricably rests on these historical sources. That's how I attempted to construct the article, and the result is a fair summation of modern, still inconsistent, thinking.

AFAIK, no modern source will verify "always, frequently, sometimes". OTOH, innumerable modern sources will count the noble gases, the halogens (F, Cl, Br, I) and H, N, O, and S as nonmetals. And a significant number will count B, Si, Ge, As, Sb, and Te as metalloids. And every now and then C, P or Se will cause hiccups (for considered reasons), as per the 2013 cite.

All that said, I've replaced the older cites in the lede image with a cite to Hawley's Condensed Chemical Dictionary, 16^th edition (2016). This reference most helpfully, relevantly, and importantly adds, "Any such list [of nonmetals] is open to challenge".

For the red-shaded metalloids, which sometimes are or aren't counted as nonmetals, I trimmed the 70s and 90s cites; kept the 2006 cite; and added a 2020 cite.

I hope this will be acceptable. I'll check the rest of the article for any knock-on editing requirements.

Physical props

Properties of metals lighter than
antimony, with iron for a comparison

Metals	Density	Strength	Electronegativity
Nonmetals	Low	Nil to low	Moderate to high
Lighter metals	Low	Low to high	Low
Heavier metals	Higher	Low to high	Low to high

Groups 1–2, Sc,
Y, Ti, V, Zr, La, Eu

Caption text

Aspect	Heavier metals	Lighter metals	Nonmetals
Density	High	Low	Low
Strength	Low to high	Low to high	Nil to low
Electronegativity	Low to high	Low to high	Mod to high

Peer review 2

Sandbh

I'm submitting this article for a second peer review in order to assess its suitability for an FAC nomination, following four unsuccessful such nominations.

Sequence of FAC nominations

The comments in the last column are my personal views. Nonmetal at FAC and FAC talk: Sequence of events Event Open Close Days ca. Words Editors Oppose Support Main concern FAC1 Jul 20 Jul 26 6 4,310 6 4 0 Request to undo close of Nonmetal Jul 27 Aug 1 5 1,517 Unstated FAC expectations PR1 Aug 2 Oct 5 64 35,360 16 FAC2 Oct 5 Oct 18 13 3,440 6 1 0 Closure of Nonmetal Oct 19 Oct 24 5 6,295 Closure before OP's responded FAC3 Oct 31 Jan 18 79 39,450 21 1 6 Closure of nonmetal FAC archive 3 Jan 19 Jan 20 1 1,752 Closure pre-opportunity to address o/s concerns FAC4 Feb 4 Feb 5 1 3,043 15 1 2 FAC4 talk Feb 4 Feb 5 1 730 Closure of nonmetal FAC archive 4 Feb 7 Closure pre-opportunity to address o/s unfounded concerns Days in FAC: 99 FAC editors: 64 (not counting me and the FAC Coord) Approx. net FAC word count: 86,470 Days between FAC 1 and 2: 71 Days between FAC 2 and 3: 13 Days between FAC 3 and 4: 17 Word count here at FAC talk: 9,564 Article word count: 6,800

At the end of each of the first three FAC nominations I acted on all o/s feedback before resubmitting. This included an extensive PR between the first two FAC nominations.

What follows are some further comments by me, and some responses to specific FAC 4 feedback organised according to the associated editor. Thank you. Sandbh (talk) 22:46, 22 February 2022 (UTC)

Sandbh

All FAC 4 feedback has been considered and acted on accordingly. I was astonished by the amount of effort that went into that feedback and will always be grateful to the editors involved.

I read Sandy Georgia's article on Achieving excellence through featured content, and Tony1's article on How to improve your writing. Some of the content in these articles comes down to stylistic differences with which I did not always agree, and I found the latter to be belaboured, and didn't finish it. Nevertheless, I get the point of such advice and applied it where I thought it would add value.

The gist of the nonmetal article can be got by reading only the topic sentence in each paragraph. The technical subject matter means there is some WP:JARGON, which I've attempted to minimise. YMMV. Sandbh (talk) 22:46, 22 February 2022 (UTC)

Jo-Jo Eumerus

• Is it absolutely necessary to have all these citations in the lead section? [while I am no fan of WP:WIAFA#2's requirement of MOS compliance, it is one of the FA criteria and Wikipedia:Manual of Style/Lead section#Citations discourages adding references to lead sections when they aren't needed, and they aren't needed here]

Thank you(!), I agree they aren't needed here and have removed them. They were originally added following previous challenges, when I wasn't aware of that nice bit of MOS guidance.

• Some sources have page numbers given and others don't - instead only featuring a "passim" even if the source is a long book.

Passim is used six times out of ca. 280 citations, for three sources. I use it when the information concerned is found in the source generally or in multiple places throughout. For example, I cite Wiberg 2001 as a source of information for the appearance and structures of the 23 nonmetals within scope of the article rather than list 23 specific page references. Sandbh (talk) 22:46, 22 February 2022 (UTC)

Licks-rocks

• The [distinguishing criteria] section also does does not seem to make any attempt to establish what the current most used criteria are, or to explain how any of the criteria suggested would work or what differences it would make. Are all of them E?

I've added a paragraph about probably the best known attempt to distinguish nonmetals from metals, and noted the shortcomings of this criterion. They're more or less E, although not necessarily I, as the article now notes:

"Kneen et al. suggested that the nonmetals could be discerned once a [single] criterion for metallicity had been chosen, adding that, "many arbitrary classifications are possible, most of which, if chosen reasonably, would be similar but not necessarily identical." Sandbh (talk) 22:46, 22 February 2022 (UTC)

Sandy Georgia

• This passage: "Fourteen elements effectively [H, O, N, and S; F, Cl, Br and I; and He, Ne, Ar, Kr, Ze, and Rn] always recognized as nonmetals…Up to a further nine elements are frequently or sometimes considered as nonmetals" What is the meaning of "effectively"? Why "frequently", in relation to such an old source? Is all of this still the case, or not? If so, an updated source would be helpful.

"Effectively" means that there are some very peculiar instances of H, N, S, I and Rn being referred to as metalloids, rather than nonmetals. I feel that these instances are so peculiar that they can be effectively ignored. The magnitude of the number of elements treated as nonmetals hasn't changed significantly since at least the 1960s.

• The prose is unnecessarily dense and jargon-filled.

I've edited the article in an attempt to reduce the density and to remove jargon where feasible.

• "Homberg's approach represented "an important move toward the modern concept of an element".[57] Subsequently, the first modern list of chemical elements was given by Lavoisier in his "revolutionary" [58] 1789 work..."

Both attributions namely [57] and [58] were there at the time.

• There are three uses of the word subsequently...

There's now one left:

"Homberg's approach represented "an important move toward the modern concept of an element".[26] Subsequently, the first modern list of chemical elements was given by Lavoisier in his "revolutionary"[27]..."

I feel this one is fine since the "subsequently" is designed to provide a thematic link.

• This looks like original research: "Since there are 118 known elements,[17] as of February 2022, the 23 nonmetals within the scope of this article are outnumbered by the metals several times." While it may be an obvious calculation of simple math, why is it in the article if not citeable to a high quality source?

Since metals and nonmetals represent the two great classes in chemistry it's there to provide some context as to the proportions involved. For example, even though there are so many metals, nonmetals nevertheless occupy the first ten places in a "top 20" table of elements most frequently encountered in 895,501,834 compounds, as listed in the Chemical Abstracts Service register for November 2021. See the Chemical section, para. 5.

• Look at Noble gases in edit mode. Why do short-note citations, which will almost never wrap, use non-breaking spaces, while something like "core may contain ca. 10¹³" does not?

I've used non-breaking spaces in short-note citations ever since receiving feedback as to the desirability of doing so during the successful 2014 FAC nomination of metalloid. The heavy metals FA (2016) likewise does so.

• One of the first things the reader encounters is a WP:GALLERY (that did nothing to enhance my comprehension of the article).

The gallery was intended to show the variety in colour and form of the nonmetals. The gallery caption now makes this clear. Sandbh (talk) 22:44, 22 February 2022 (UTC)

Sequence

https://en.wikipedia.org/wiki/User:SandyGeorgia/Achieving_excellence_through_featured_content https://en.wikipedia.org/wiki/User:Tony1/How_to_improve_your_writing 9,214 words; 94,724 bytes

Nonmetal at FAC and FAC talk: Sequence of events

Event	Open	Close	Days	ca. Words	Editors	Oppose	Support	Main concern
FAC1	Jul 20	Jul 26	6	4,310	6	4	0
Request to undo close of Nonmetal	Jul 27	Aug 1	5	1,517				Unstated FAC expectations
PR1	Aug 2	Oct 5	64	35,360	16
FAC2	Oct 5	Oct 18	13	3,440	6	1	0
Closure of Nonmetal	Oct 19	Oct 24	5	6,295				Closure before OP's responded
FAC3	Oct 31	Jan 18	79	39,450	21	1	6
Closure of nonmetal FAC archive 3	Jan 19	Jan 20	1	1,752				Closure pre-opportunity to address o/s concerns
FAC4	Feb 4	Feb 5	1	3,043	15	1	2
FAC4 talk	Feb 4	Feb 5	1	730
Closure of nonmetal FAC archive 4	Feb 7							Closure pre-opportunity to address o/s unfounded concerns

Days in FAC: 99
FAC editors: 64 (not counting me and the FAC Coordinator)
Approx. net FAC word count: 86,470
Days between FAC 1 and 2: 71
Days between FAC 2 and 3: 13
Days between FAC 3 and 4: 17
Word count at Talk:Featured article candidates: 9,564
Article word count: 6,800

Proposed changes to FAC system
Proposed system changes
Aug 3 to Aug 8

Nonmetal

Wikipedia:Featured_article_candidates/Nonmetal/archive4

Jo-Jo Eumerus

• Is it absolutely necessary to have all these citations in the lead section? [while I am no fan of WP:WIAFA#2's requirement of MOS compliance, it is one of the FA criteria and Wikipedia:Manual of Style/Lead section#Citations discourages adding references to lead sections when they aren't needed, and they aren't needed here]
• Some of the footnotes contain claims that need to be sourced.
• Some sources have page numbers given and others don't - instead only featuring a "passim" even if the source is a long book.
  • Passim is used seven times out of 267 citations. I use it when the information concerned is found in the source generally or in multiple places throughout the work. For example, I cite Wiberg 2000 as a source of information for the appearance and structures of the 23 nonmetals within scope of the article rather than list 23 specific page references.
• "elemental selenium is occasionally found" and the second paragraph of the chemical sections is unsourced.

Licks-rocks

• I am a bit confused by the distinguishing criteria section. the combination of a (seemingly largely unnecessary) quote, infobox, bullet list and enumeration make it very cluttered.
• The section also does does not seem to make any attempt to establish what the current most used criteria are, or to explain how any of the criteria suggested would work or what differences it would make. Are all of them E?

SandyGeorgia

• Black phosphorus copyvio
• WP:NOPRICE
• Other odd citation issues, eg, "Johnson[37] noted that physical properties can best indicate the metallic or nonmetallic properties of an element, with the proviso that other properties will be needed in a number of ambiguous cases." (If Johnson noted all of this, why isn't the citation at the end of the sentence?)
• This whole passage is cited to a 1966 source: "Fourteen elements effectively always recognized as nonmetals are hydrogen, oxygen, nitrogen, and sulfur; the corrosive halogens fluorine, chlorine, bromine, and iodine; and the noble gases helium, neon, argon, krypton, xenon, and radon. Up to a further nine elements are frequently or sometimes considered as nonmetals, including carbon, phosphorus, and selenium; and the elements otherwise commonly recognized as metalloids namely boron; silicon and germanium; arsenic and antimony; and tellurium, bringing the total up to twenty-three nonmetals.[4]" Why source to something that old? What is the meaning of "effectively", especially in relation to a more than 50-year-old source? Why "frequently", in relation to such an old source? Is all of this still the case, or not? If so, an updated source would be helpful.

Prose

The prose is unnecessarily dense and jargon-filled. Some samples only:

• The distinguishing criteria section has a long-list of red-linked terms that are never defined (anywhere in the article, or anywhere on Wikipedia). This renders the text a mystery to layreaders.
• One sample paragraph for examination:

  The term "nonmetallic" dates from as far back as 1708 when Wilhelm Homberg mentioned "non-metallic sulfur" in his Des Essais de Chimie.[56] He had refuted the five-fold division of matter into sulfur, mercury, salt, water and earth, previously in vogue, as postulated by Étienne de Clave [fr] (1641) in New Philosophical Light of True Principles and Elements of Nature. Homberg's approach represented "an important move toward the modern concept of an element".[57] Subsequently, the first modern list of chemical elements was given by Lavoisier in his "revolutionary"[58] 1789 work Traité élémentaire de chimie in which he distinguished between simple metallic and nonmetallic substances. In its first seventeen years, Lavoisier's work was republished in twenty-three editions and six languages, and carried his "new chemistry" across Europe and America.[59]

• There are three uses of the word subsequently (always a tipoff to other prose issues); in this case, they are all either confusing, or point two things that only could have happened afterwards, hence redundant. Looking at one of those:
  • "The discovery of a quasi-spherical allotropic molecule, borospherene (B40), was announced in 2014. Silicon was most recently known only in its crystalline and amorphous forms. The synthesis of an orthorhombic allotrope, Si24, was subsequently reported in 2014." I can't decipher what this text even means, much less the circular reasoning on 2014, most recently, and back to 2014.
  • The other two instances of subsequently (It can lose its single valence electron in aqueous solution, leaving behind a bare proton with tremendous polarizing power.[80] This subsequently attaches itself to the lone electron pair of an oxygen atom in a water molecule,) and (The term "nonmetallic" dates from as far back as 1708 ... Subsequently, the first modern list of chemical elements was given by Lavoisier) are examples of convoluted prose and issues that could not have happened before the first, hence redundant.
• This looks like original research: "Since there are 118 known elements,[17] as of February 2022, the 23 nonmetals within the scope of this article are outnumbered by the metals several times." While it may be an obvious calculation of simple math, why is it in the article if not citeable to a high quality source?
• There are unattributed quotes throughout.
• The distinction between metals and nonmetals arose, in a convoluted manner,

These are samples only; similar is spotted wherever the eye falls.

MOS issues

• Incorrect use of "Main" hatnotes. For example, (oddly) the halogen article never mentions nonmetal, so the content in this article cannot be a summary of that article.
• MOS:ELLIPSES
• Look at Noble gases in edit mode. Why do short-note citations, which will almost never wrap, use non-breaking spaces, while something like "core may contain ca. 10¹³" does not?
• MOS:WAW: The term "nonmetallic" dates from ...
• 2 Concept origin, distinguishing criteria, and use of term as a section heading, followed by the exact same words at 2.1 Origin of the concept, 2.2 Distinguishing criteria, 2.3 Use of the term (don't repeat words at lower levels)

This is not an exhaustive list; these suggest a MOS review has not been done.

Presentation

• One of the first things the reader encounters is a WP:GALLERY (that did nothing to enhance my comprehension of the article).
• The juxtaposition of an indented long list with a quote box in the Distinguishing criteria section is visually awful, and I wonder what our screenreading users might say about it. Why isn't that example algorithm prosified ? Why "example" (as in, which sources disgree and have other examples)?

Talk
I wrote User:SandyGeorgia/Achieving excellence through featured content mostly for medical editors, but the recommendations in the "Advice for FA aspirants" section works for everyone.

ComplexRational

Also, in my opinion, this has been rushed into FAC4 and several editors have raised valid concerns, so I would strongly recommend working on the article outside FAC and perhaps send it through peer review again before coming back here. While I'm all for trying again in principle, I get the impression that this is the third time it's rushed back into FAC after a closed nomination and that won't sit well with some reviewers. I sincerely believe the article has potential to reach FA, and don't feel like opposing on these grounds alone, but rushing improvements and re-nominations won't do it any good. ComplexRational (talk) 15:46, 5 February 2022 (UTC)

ANI

I concur with the above sequence of events but not the interpretation and omissions.

A. As El_C noted, posting what DePieP posted into the RfC statement before the Vote section was inappropriate.[1]

C. I did not "change" DePiep’s post, I manually reverted it and moved it into the discussion section and, in response to DePiep’s question/concern about Voting, I replied as follows: "I put the rfc as a question. A "vote" then is an expression of one's wish or choice with respect to the question."[2] DePiep ignores BRD, reverts my revert,[3] and posts an incivil "serious warning" to my talk page.[4]

D. I reverted DePiep’s contribution to the RfC since it was a commentary on the reasons for my vote, posted straight after my vote.[5] That was my bad, as El_C noted.[6], as ack by me.[7] DePiep ignores BRD and reverts my revert.

As DePiep noted, I asked him to add comments or discussion to the Votes section, in this edit[8] summary, a request which he has ignored. Sandbh (talk) 06:45, 23 January 2022 (UTC)

Alleged interference in RfC by DePiep

I regret the need to be here but this matter concerns a currently open RfC.

I recently initiated an RfC.[9] After the RfC statement section itself, there is a subsection for Votes and a subsection for Talk, notes, questions, suggestions.

User:DePiep then posted a question to the RfC statement section itself.[10]

I effectively boldly reverted DePeip’s edit by moving his question to the RfC Talk, notes, questions, suggestions subsection, and added my answer to his question.[11] I also asked DePiep to, “Please do not edit my rfc statement” adding that the place for questions is the RfC Talk etc. sub-section.

DePiep has now reverted my revert[12] and added a “serious warning” to my talk page,[13] saying he is surprised to have to tell me, once more, on how to behave in a discussion; that my revert of his edit was unacceptable, including my “misleading” edit summary; that I’ll understand this is tearing his patience with me and my editing behaviour; that there are other paths for me to walk if I have questions or issues “(but not me is gonna point them out to you any more)”. Further, "I will not accept you breaking or spoiling a discussion. So best consider this as a serious warning."

DePiep has also added a Glossary to the RfC statement section itself, without consulting me as the initiator of the RfC, and ignoring my previous request to please not edit my RfC statement.

In bringing my allegations here I am only looking to run the RfC free from interference of this kind by DePiep, and to be free from incivil postings to my talk page.

If this is an inappropriate forum to raise allegations and concerns of this nature I will be happy to raise them via another avenue.

Thank you. I’ve tried to be polite. If I’m at fault I am happy to be corrected. Sandbh (talk) 10:05, 22 January 2022 (UTC)

I will reply later on. Most clarifying diffs will be from the RfCs history. -DePiep (talk) 11:01, 22 January 2022 (UTC)

Update: DePiep has now added commentary immediately after my vote, rather than adding such comments to the Talk, notes, questions, suggestions subsection.[14]. I thanked him for this edit and then boldly reverted it, saying, “Please do not add comments or discussion to the Votes section”.[15] DePiep reverted my revert, commenting, “"it is a discussion. Read WP:RFC. Do not change my edits. Stop tit-for-tat."[16]. While I stand ready to be corrected, I regard these alleged actions by DePiep as a form of vandalism, misguided as it may be. Sandbh (talk) 11:17, 22 January 2022 (UTC)

FAC nom

This is my third outing at FAC for this vital article. The subject matter is one half of the fundamental distinction made in chemistry between metals and nonmetals.

Following FAC #2:

• the lede has been trimmed down to four paragraphs;
• nine images, tables or quote boxes have been removed or integrated into the text; and
• ca. 150 minor edits have been made to improve the article.

Please note that addressing the nature of nonmetals necessitates a fair amount of descriptive, list-like content. Where feasible I've sought to avoid long, list-like sentences by instead using dot point lists or summary tables.

As suggested at FAC #2, here's my assessment against the FAC criteria.

Assessment

It is: well-written: its prose is engaging and of a professional standard; That's been my aim. Each paragraph in the article addresses one idea, as flagged by its lead sentence. The logical flow of the article can then be grasped by reading only each first sentence. As requested at FAC #2, the article has been subject to a formal copy edit. I did this by starting at its end, and working back up to the start, making adjustments along the way. comprehensive: it neglects no major facts or details and places the subject in context; That's certainly the case. well-researched: it is a thorough and representative survey of the relevant literature; claims are verifiable against high-quality reliable sources and are supported by inline citations where appropriate; I doubt there's a more focused encyclopedic and citation supported survey of nonmetals anywhere. neutral: it presents views fairly and without bias; There's some variability in the literature as to which chemical elements are nonmetals. I've attempted to take a balanced approach to this question, and to make this consideration explicit in the article. stable: it is not subject to ongoing edit wars and its content does not change significantly from day to day, except in response to the featured article process; It's certainly that. compliant with Wikipedia's copyright policy and free of plagiarism or too-close paraphrasing. To the best of my ability that's the case. It follows the style guidelines, including the provision of: a lead: a concise lead section that summarizes the topic and prepares the reader for the detail in the subsequent sections; Check. The lead focuses on only the most important ideas. appropriate structure: a substantial but not overwhelming system of hierarchical section headings; Check. consistent citations: where required by criterion 1c, consistently formatted inline citations using footnotes—see citing sources for suggestions on formatting references. Citation templates are not required. Check. Media. It has images and other media, where appropriate, with succinct captions and acceptable copyright status. Images follow the image use policy. Non-free images or media must satisfy the criteria for inclusion of non-free content and be labeled accordingly. An image check was conducted and passed at FAC #2. The article has no new images. All images bar one have succinct captions. The exception is the "Periodic table extract" image which needs an extended caption in order to explain the features it (the image) is encapsulating. I've considered moving the bulk of the content of the caption into the text however I feel that to do so would make it harder to unpack the image. Length. It stays focused on the main topic without going into unnecessary detail and uses summary style. The number of endnotes has been criticised in past FAC's. Consistent with Help:Explanatory notes I generally use endnotes to elaborate items which would otherwise seem to make the main body text too detailed for the general reader. At the same time, the footnotes may appeal to the specialist reader. For a technical subject of this kind, I feel this is a good way of addressing FA criterion 1c, "it is a thorough and representative survey of the relevant literature." This is particularly the case for descriptive chemistry in which, unlike the laws of physics, there are always exceptions. Of the 66 endnotes, 40% belong to images or tables.

I thank numerous peer- and FAC-reviewers for previous feedback on the article.

Sandbh (talk) 06:55, 30 October 2021 (UTC)

Nonmetal halogens

• "It will be seen that these elements of zero valence and no chemical character form a natural passage from the strongly electro-negative non-metallic halogens…"

— A review of some of the recent literature of the periodic law, RH Bradbury - Journal of the Franklin Institute, 1902

• "In the decidedly nonmetallic halogen group…"

— Qualitative analysis as a laboratory basis for the study of… Page 64, William Conger Morgan · 1906

• "And among the nonmetallic halogens we find the…"

— Recent Advances in Physical and Inorganic Chemistry - Page 245, Alfred Walter Stewart · 1920

• "In a similar manner the nonmetal halogen elements are arranged"

— Essentials of Chemistry - Page 54, Luros G · 1955

• "The alkali metals of Group la combine readily with the nonmetal halogens of Group VIIa."

— General Chemistry - Page 87, John Arrend Timm · 1966

---

• "Nitrogen was the subject of Chapter 15, and the nonmetallic halogens, of Chapter 17."

— Introduction to Chemistry - Page 226, Williams et al. · 1973

• "The electron configurations of atoms of some of the elements, the alkali metals and the nonmetallic halogens and noble gases , are given in Table 4-1."

— Geology: Our Physical Environment, Page 30, Davis et al. 1976

• "The nonmetallic halogen atoms easily pick up an electron , thus forming halide ions."

— Chemistry Decoded - Page 346, Leonard W. Fine · 1976

• "Iodine is a nonmetallic halogen , having the lowest reactivity of any substance in this group."

— Properties of Nonmetallic Fluid Elements - Volume 3, Part 2 - Page 115, Yeram Sarkis Touloukian, ‎Cho Yen Ho · 1981 · ‎p. 115

• "An activity series for the nonmetallic halogens was given in Chapter 6."

— Understanding Chemistry - Page 386, Robert J. Ouellette · 1987

---

• "Other properties are similar to those of the nonmetallic halogen elements in Group VIIA or 17 in the second column from the far right of the table…in this case, the nonmetal halogen element is reduced to its halide ion."

— Chemistry: A Basic Introduction - Pages 125, 271, George Tyler Miller · 1987

• "Iodine resembles bromine because they are nonmetallic halogens that form compounds like those of chlorine."

— Chemistry - Page 8, Nathan · 1993, p. 8

• "What causes gold to emulate many properties of the nonmetallic halogens?"

— Chemical Principles, Page 549, Steven S. Zumdahl · 1995

• "...but we must not forget the novel involvement of the non-metal halogens."

— The Chemistry of Evolution: The Development of our Ecosystem, R.J.P Williams, ‎J.J.R Fraústo da Silva · 2005

• "Among the other nonmetal halogens used to partially halogenate metal oxides…"

— Inorganic Reactions and Methods, The Formation of Bonds to…, A. P. Hagen · 2009, p. 221

---

• "Non-metallic halogens such as chlorine, iodine and bromine are salt-forming elements."

— "TRPM7 is regulated by halides through its kinase domain", H Yu, Z Zhang, A Lis, R Penner, A Fleig - Cellular and molecular life… 2013

• "Nonmetallic halogen element of atomic number 53…

— Hawley's Condensed Chemical Dictionary - Page 765, Michael D Larrañaga, ‎Richard J. Lewis, Sr., ‎Robert A. Lewis · 2016

• "Non-metallic halogens are very attractive"

— "Hydrothermal preparation of visible-light-driven Br-doped Bi₂WO₆ photocatalyst", P Dumrongrojthanath, A Phuruangrat, S Thongtem… Materials Letters, 2017 - Elsevier

• "…chlorine; element #17; a nonmetal halogen gas"

— Trauma, 8th Edition - Page 1139, Moore et al. 2017, p. 1139

• "…and a more detailed grouping in families of: alkali Earth, alkaline Earth, transition metal, rare Earth, other metal, metalloid, and nonmetal halogen to noble gas."

— Illustrated Encyclopedia of Applied and Engineering Physics, Robert Splinter · 2017, p. 382

Ions (aq)

Element (atomic number, symbol, name)			Cation species (C)	Oxycation species (xC)	Anion species (A)	Oxyanion species (xA)	Notes	Summary of species
1	H	Hydrogen	H+					1: C
2	He	Helium						(0)
3	Li	Lithium	Li+					1: C
4	Be	Beryllium	Be2+	BeOH+ Be2OH3+ Be3(OH)33+		Be(OH)3− Be(OH)42−		3: C, xC, xA
5	B	Boron				Borates		1: xA
6	C	Carbon				CO 32−		1: xA
7	N	Nitrogen				NO 2− NO 3−		1: xA
8	O	Oxygen			OH−			1: A
9	F	Fluorine			F−			1: A
10	Ne	Neon						(0)
11	Na	Sodium	Na+					1: C
12	Mg	Magnesium	Mg2+	Mg(OH)+ Mg4(OH)44+				2: C, xC
13	Al	Aluminium	Al3+	Al(OH)2+ Al(OH)+ 2 Al 2(OH)4+ 2 Al 3(OH)5+ 4		Aluminates		3: C, xC, xA
14	Si	Silicon				Silicates		1: xA
15	P	Phosphorus				P(H)O 32− phosphites PO 43− polyphosphates		1: xA
16	S	Sulfur			HS−	SO 32− SO 42−		2: A, xA
17	Cl	Chlorine			Cl−	ClO 4−		2: A, xA
18	Ar	Argon						(0)
19	K	Potassium	K+					1: C
20	Ca	Calcium	Ca2+	CaOH+				2: C, xC
21	Sc	Scandium	Sc3+	Sc(OH)2+ Sc(OH)2+ Sc2(OH)44+ Sc3(OH)54+		Sc(OH)42−		3: C, xC, xA
22	Ti	Titanium	Ti3+ (violet)	Ti(OH)2+ Ti2(OH)24+ Ti(OH)3+		titanates		3: C, xC, xA
23	V	Vanadium	V2+ (violet) V3+ (green)	V(OH)2+ V(OH)2+ VO2+ (blue) VO(OH)+ VO 2+ (yellow)		VO2(OH)2− VO 43− vanadates		3: C, xC, xA
24	Cr	Chromium	Cr2+ (blue-green) Cr3+ (green)	Cr(OH)2+ Cr(OH)2+ Cr2(OH)24+ Cr3(OH)45+		CrO 42− (yellow) Cr 2O 72− (orange)		3: C, xC, xA
25	Mn	Manganese	Mn2+ (faint pink)	Mn(OH)+ Mn2(OH)3+ Mn(OH)2+		MnO 42− (green) MnO 4− (purple)		3: C, xC, xA
26	Fe	Iron	Fe2+ (green) Fe3+ (violet)	Fe(OH)+ (green) Fe(OH)2+ Fe(OH)+ 2 (yellow-brown) Fe2(OH)24+ Fe3(OH)45+		Fe(OH)3− FeO 42− (red-purple)		3: C, xC, xA
27	Co	Cobalt	Co2+ (pink) Co3+ (blue-green)	Co(OH)+ (pink) Co2(OH)3+ Co4(OH)43+		Co(OH)42−		3: C, xC, xA
28	Ni	Nickel	Ni2+ (green)	Ni(OH)+ Ni2(OH)2+ Ni4(OH)44+		Ni(OH)3−		3: C, xC, xA
29	Cu	Copper	Cu+ Cu2+ (blue)	Cu(OH)+ Cu2(OH)22+		Cu(OH)3− Cu(OH)42−		3: C, xC, xA
30	Zn	Zinc	Zn2+	Zn(OH)+ Zn2(OH)3+		Zn(OH) 3− Zn(OH) 42− Zn2(OH)62−		3: C, xC, xA
31	Ga	Gallium	Ga3+	Ga(OH)2+ Ga(OH)2+		Ga(OH)− 4		3: C, xC, xA
32	Ge	Germanium				GeO(OH) 3− Ge2(OH)22− germanates		2: xC, xA
33	As	Arsenic			H2As−	As(OH)4− AsO 33− AsO 43−		2: A, xA
34	Se	Selenium			HSe−	SeO 32− polymeric species SeO 42−		2: A, xA
35	Br	Bromine			Br−	BrO 3− BrO 4−		2: A, xA
36	Kr	Krypton						(0)
37	Rb	Rubidium	Rb+					1: C
38	Sr	Strontium	Sr2+	SrOH+				2: C, xC
39	Y	Yttrium	Y3+	Y(OH)2+ Y(OH)2+ Y2(OH)24+ Y2(OH)35+		Y(OH)4−		2: C, xC
40	Zr	Zirconium		Zr(OH)3+ Zr 4(OH)8+ 4				1: xC
41	Nb	Niobium				polymeric niobates		1: xA
42	Mo	Molybdenum	Mo3+			MoO 42− isopolyanions		3: C, xC, xA
43	Tc	Technetium				TcO(OH) 3−		2: xC, xA
44	Ru	Ruthenium	Ru2+ (pink) Ru3+ (yellow-red)			RuO 43− RuO 4−	&	3: C, xC, xA
45	Rh	Rhodium	Rh3+ (yellow)	RhOH2+			&	3: C, xC, xA
46	Pd	Palladium	Pd2+ (red-brown)	PdOH+			&	2: C, xC
47	Ag	Silver	Ag+			Ag(OH)− 2		2: C, xA
48	Cd	Cadmium	Cd2+	Cd(OH)+ Cd2OH3+ Cd4(OH)44+		Cd(OH) 3− Cd(OH)2− 4		3: C, xC, xA
49	In	Indium	In3+	InOH2+ In(OH)2+		In(OH)3− 6		3: C, xC, xA
50	Sn	Tin	Sn2+	SnOH+ Sn2(OH)22+ Sn3(OH)42+		Sn(OH)3− Sn(OH) 62−		3: C, xC, xA
51	Sb	Antimony		Sb(OH) 2+		Sb(OH) 4− Sb(OH) 6− antimonates		2: xC, xA
52	Te	Tellurium		Te(OH) 3+	HTe− Te2−	TeO(OH)3− TeO2(OH)23− TeO(OH)5− TeO2(OH)32− TeO3(OH)33−		3: xC, A, xA
53	I	Iodine		I(OH)+6	I−	IO 3− IO−4 + 2H2O ⇌ IO3(OH)2−3 + H+		2: A, xA
54	Xe	Xenon				XeO4− 6		1: xA
55	Cs	Caesium	Cs+					1: C
56	Ba	Barium	Ba2+	Ba(OH)+				2: C, xC
57	La	Lanthanum	La3+	La(OH)2+				2: C, xC
58	Ce	Cerium	Ce3+	Ce(OH)2+ Ce(OH) 22+ (orange)				2: C, xC
59	Pr	Praseodymium	Pr3+ (green)	Pr(OH)2+				2: C, xC
60	Nd	Neodymium	Nd3+ (lilac)	Nd(OH)2+		Nd(OH)−4		2: C, xC
61	Pm	Promethium	Pr3+ (pink)	Pr(OH)2+				2: C, xC
62	Sm	Samarium	Sm2+ (red) Sm3+ (yellow)	Sm(OH)2+				2: C, xC
63	Eu	Europium	Eu2+ Eu3+ (pale pink)	Eu(OH)2+				2: C, xC
64	Gd	Gadolinium	Gd3+	Gd(OH)2+		Gd(OH)−4		2: C, xC
65	Tb	Terbium	Tb3+ (pale pink)	Tb(OH)2+				2: C, xC
66	Dy	Dysprosium	Dy3+ (yellow)	Dy(OH)2+		Dy(OH)−4		2: C, xC
67	Ho	Holmium	Ho3+ (yellow)	Ho(OH)2+				2: C, xC
68	Er	Erbium	Er3+ (yellow)	Er(OH)2+		Er(OH)−4		2: C, xC
69	Tm	Thulium	Tm3+ (pale green)	Tm(OH)2+				2: C, xC
70	Yb	Ytterbium	Yb2+ (green) Yb3+	Yb(OH)2+		Yb(OH)−4		2: C, xC
71	Lu	Lutetium	Lu3+					2: C, xC
72	Hf	Hafnium		Hf(OH)3+		polymeric species		1: xC
73	Ta	Tantalum				tantalates		1: xA
74	W	Tungsten				WO2− 4 tungstates		1: xA
75	Re	Rhenium				ReO2− 4		1: xA
76	Os	Osmium				[OsO 2(OH) 4]2− (purple) [OsO 4(OH) 2]2−	&	1: xA
77	Ir	Iridium		Ir(OH)2+ Ir(OH)+2		polymeric species	&	1: xA
78	Pt	Platinum	Pt2+ (yellow)			polymeric species	&	2: C, xA
79	Au	Gold	Au3+	Au(OH)2+ Au(OH)+2		Au(OH)−4 Au(OH)2−5	&	2: C, xA
80	Hg	Mercury	Hg2+ Hg2+ 2	Hg(OH)+ Hg2(OH)3+		HgOH3− 3		2: C, xA
81	Tl	Thallium	Tl+	TlOH2+ Tl(OH)2+		Tl(OH)−4		3: C, xC, xA
82	Pb	Lead	Pb2+	Pb(OH)+ Pb2(OH)3+ Pb4(OH)4+4		Pb(OH)−3		3: C, xC, xA
83	Bi	Bismuth	Bi3+	Bi(OH)2+ Bi(OH)+2		Bi(OH)−4 polymeric species		2: C, xC
84	Po	Polonium	Po2+ (pink)	Po(OH)2+ 2 (yellow) Po(OH)+ 3 (yellow)	Po2−	PoO2− 3 (pink)		4: C, xC, A, xA
85	At	Astatine	At+	AtO+	At−	AtO(OH)− 2 AtO− 3 AtO− 4		4: C, xC, A, xA
86	Rn	Radon		HRnO+ 3		HRnO− 4		2: xC, xA
87	Fr	Francium	Fr+					1: C
88	Ra	Radium	Ra2+	RaOH+				2: C, xC
89	Ac	Actinium	Ac3+	AcOH2+				2: C, xC
90	Th	Thorium	Th4+	Th(OH)3+ Th(OH)22+ Th(OH)2+2 Th2(OH)6+2		polymeric species		2: C, xC
91	Pa	Protactinium	Pa3+ Pa4+	PaOH3+ Pa(OH)2+2 Pa(OH)+3 PaO+2				2: C, xC
92	U	Uranium	U3+ (purple) U4+ (green)	U(OH)3+ UO2+2 UO2OH+ (UO2)2(OH)2+2		poymeric species uranates		3: C, xC, xA
93	Np	Neptunium	Np3+ (purple) Np4+ (green)	NpO+ 2 (green) NpO2+ 2 (purple) NpOH3+ Np(OH)22+ NpO2OH+		[NpO 4(OH) 2]3− (green) NpO2OH−		3: C, xC, xA
94	Pu	Plutonium	Pu3+ Pu4+	PuO2+ 2 (orange) PuO2OH+ PuOH2+ Pu(OH)2+		[PuO 4]2− (light brown) PuO2(OH)3−		3: C, xC, xA
95	Am	Americium	Am3+ (pink)	AmO2+ 2 (yellow) AmO2+ AmOH2+ Am(OH)2+		[AmO 2(OH) 4]2−		3: C, xC, xA
96	Cm	Curium	Cm3+ (yellow)	CmOH2+ Cm(OH)2+				2: C, xC
97	Bk	Berkelium	Bk3+ (green) Bk4+ (yellow)					1: C
98	Cf	Californium	Cf2+ Cf3+ (green)					1: C
99	Es	Einsteinium	Es2+ Es3+ (pale pink)					1: C
100	Fm	Fermium	Fm2+ Fm3+					1: C
101	Md	Mendelevium	Md2+ Md3+					1: C
102	No	Nobelium	No2+ No3+					1: C
103	Lr	Lawrencium	Lr3+					1: C
104+	Rf+	Rutherfordium & beyond						(0)

Groups that bridge blocks

Sc, Y, La, Ac, Zr, Hf, Rf, Nb, Ta, Db, Lu, Lr, Cu, Ag, Au, Zn, Cd, Hg, He, Ne, Ar, Kr, Xe, Rn

Hydrogen

Helium

Lithium

Beryllium

Boron

Carbon

Nitrogen

Oxygen

Fluorine

Neon

Sodium

Magnesium

Aluminium

Silicon

Phosphorus

Sulfur

Chlorine

Argon

Potassium

Calcium

Scandium

Titanium

Vanadium

Chromium

Manganese

Iron

Cobalt

Nickel

Copper

Zinc

Gallium

Germanium

Arsenic

Selenium

Bromine

Krypton

Rubidium

Strontium

Yttrium

Zirconium

Niobium

Molybdenum

Technetium

Ruthenium

Rhodium

Palladium

Silver

Cadmium

Indium

Tin

Antimony

Tellurium

Iodine

Xenon

Caesium

Barium

Lanthanum

Cerium

Praseodymium

Neodymium

Promethium

Samarium

Europium

Gadolinium

Terbium

Dysprosium

Holmium

Erbium

Thulium

Ytterbium

Lutetium

Hafnium

Tantalum

Tungsten

Rhenium

Osmium

Iridium

Platinum

Gold

Mercury (element)

Thallium

Lead

Bismuth

Polonium

Astatine

Radon

Francium

Radium

Actinium

Thorium

Protactinium

Uranium

Neptunium

Plutonium

Americium

Curium

Berkelium

Californium

Einsteinium

Fermium

Mendelevium

Nobelium

Lawrencium

Rutherfordium

Dubnium

Seaborgium

Bohrium

Hassium

Meitnerium

Darmstadtium

Roentgenium

Copernicium

Nihonium

Flerovium

Moscovium

Livermorium

Tennessine

Oganesson

32-column periodic table showing, from left to right, the location of group 3; the heavy group 4 and 5 elements; lutetium and lawrencium; groups 11–12; and the noble gases

On the group 12 metals (zinc, cadmium and mercury), Smith observed that, "Textbook writers have always found difficulty in dealing with these elements." A 2003 survey of chemistry books showed that they were treated as either transition metals or main group elements on about a 50/50 basis. They are sometimes regarded as linking the d block to the p block. Notionally they are d block elements but they have few transition metal properties and are more like their p block neighbors in group 13. In a like manner, the relatively inert noble gases, in group 18, bridge the most reactive groups of elements in the periodic table—the halogens in group 17 and the alkali metals in group 1.

Chemically, the group 3 elements, lanthanides, and heavy group 4 and 5 elements show some behaviour similar to the alkaline earth metals or, more generally, s block metals but have some of the physical properties of d block transition metals.

Meanwhile, lutetium (at the end of the f-block) behaves chemically as a lanthanide (with which it is often classified) but shows a mix of lanthanide and transition metal physical properties (as does yttrium). Lawrencium, as the heavier congener of lutetium, would presumably display like characteristics. The coinage metals in group 11 (copper, silver, and gold) are chemically capable of acting as either transition metals or main group metals.

Notes

References

Park

Aesthetics and symmetry

Introduction

As promised, here is a discussion on the (non-)relevance of aesthetics and regularity in the context of the Group 3 question. It is taken and adapted from my peer-reviewed open access articlewhich now has 400 accesses, in Foundations of Chemistry. The editor is Eric Scerri, who is also the chair of the IUAPC Group 3 project.

I caution readers to not confuse Eric's personal view on the group 3 question with his role as the editor of FoC, nor with his role as the chair of the IUPAC project.

My conclusion is that, akin to a game of whack-a-mole, attempts to improve regularity in the appearance of the periodic table increases the number of irregularities amongst various other properties and relationships across the table, and cognitive dissonance with respect to chemical relationships between or within groups or series of elements. Further, while Nature does not care about aesthetics, the composition of Group 3 as Sc–Y–La–Ac appears to be more consistent with the texture of the world.

Scerri sets the scene

Scerri (2008, p. 57) has argued for lutetium under yttrium (and helium over beryllium), since the periodic table can then be arranged, from a philosophical point of view, so that it shows the greatest degree of regularity and symmetry. Such a table may better reflect the regularity of the periodic law. He cites as an example, the left-step or Janet periodic table (Fig. 9). Such a table facilitates a regular array of vertical triads (Fig. 10), in which the middle element of the triad has an atomic number that is the average of those of the first and third elements. Scerri does not support lanthanum under yttrium since, in a 32-column table, and on the basis of regularity and symmetry, this once again results in awkward split d-block (Fig. 11).^[n13]

n13: Hamilton (1965) shows a periodic table extract (Groups 1 to 11, plus footnoted lanthanoids and actinoids, showing Ce, Pr…Lu; and Th, Pa…Lw) with a split d-block (the gap is between Groups 3 and 4) and says that—without any fuss—this is “the periodic table as it is usually presented”. Reger et al. (2010, p. 295) write that “perhaps” the correct shape of the 32-column periodic table should feature a split d-block given the electron configurations of La and Ac, but that “we avoid these structures by splitting the f-block from the rest of the periodic table. This also has the advantage of being able to print a legible periodic table on a single piece of paper.” (They show La below Y in the rest of their book.)

In a similar vein, Scerri (2020b, p. 5) notes that with respect to the 32-column form, “After any new insights are gained, one can well return to the 18-column format with deepened knowledge.”

The split-d table dates from as early as 1934 (Romanoff). It was the table of choice for van Spronsen (1969) in his history of the first hundred years of the periodic system of chemical elements.

Scerri's argument remains inconclusive

His argument remains inconclusive as there is no basis to regard regularity or symmetry as fundamental requirements (Scerri 2004, p. 149; 2019, p. 385). Stewart (2018b, p. 75) observed that, “Triads are a consequence of the structure of the system and cannot at the same time be its cause.” Scerri (2020a, pp. 387, 401) acknowledges that we should be aware of arguments based on regularity or symmetry. Jensen (2019), whose 1982 article in the Journal of Chemical Education kicked off the debate on the composition of Group 3, recently attacked the relevance of [vertical] triads.

Curiously, as discussed later in this article, increasing regularity in the shape of the periodic table increases the number of irregularities amongst various other properties and relationships across the table.^[n14] Indeed, as Imyanitov (2016, pp. 153–154) observed: If one seeks for the maximum chemical utility…[one] should opt for the more ‘unruly’ tables. If one seeks maximum elegance and orderliness above all…[one] should favor the more regular representations.

n14: A simple example is to rearrange the line of elements shown on the cover of Bent’s (2006) monograph, into the conventional 18-column layout with the two Group 3 options, as follows:

[here].

The historical obsession with symmetry

The obsession of the Greeks with the concept of symmetry retarded progress in astronomy for at least 1500 years (Yang 1996, p. 271). They perpetuated the idea of the Harmony of the Spheres and the Dogma of the Circles. According to these works, the heavenly bodies must observe the most symmetrical rules, and the circle and the sphere are the most symmetrical forms. But the heavenly bodies do not make simple circular motions. So they tried to fit their motions with circular ones superposed on circular ones. When that did not work either, they tried circular ones on circular ones on circular ones, and so on.

My shock and realisation

The first time I saw a 32-column table with a split d-block (Fig. 11) I thought it must have been “wrong” since it appeared so awkward; I later came to realise that I’d subconsciously adopted the Western cultural obsession with symmetry.^[n15] Jensen earlier referred to the abuse of (Platonic) symmetry considerations in the construction and interpretation of periodic tables in general, including to the extent of triumphing over the inconvenient facts of chemistry (Jensen 1986, passim; 2003, pp. 953–954).

n15: In a related manner, notions of beauty and ugliness show some variation across time, and between cultures and people (Shiraev and Levy 2013, p. 102). For example:

• Mountains are seen as sublime expressions of nature; only two hundred years ago they were regarded as loathsome things to be avoided at all costs (Bayley 2015).

• Two years before it was finished, the great Paris “intellos” of the day lined up in opposition to the Eiffel Tower, writing letters to the papers denouncing it as an ugly and hateful column of bolted tin; of course, it is now one of the world’s most beloved monuments (Bayley 2015).

• Foreigners in Japan were known to refer to a good deal of ikebana (flower arrangement) as unattractive (Shiraev and Levy 2013, p. 102).

The ACS Division of Inorganic Chemistry had been using a split-d table as its e-mail header, without any concerns being raised, as far as I know, on ugliness or disorderliness. It looks engaging to my subjective eye—ordered, yet with intriguing flourishes:

[here]

Scerri (2020b, p. 11) reports that the logo was withdrawn due to the controversy associated with the Group 3 question. It has subsequently been reinstated.

Symmetry breaking

An emerging field of thought is the importance of symmetry breaking,^[n16] rather than pure symmetry:

…symmetries matter, largely because we like to see them broken sometimes: the laws, particles and forces of physics all have their roots in symmetry-breaking. They create what David Gross of the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara, calls the “texture of the world”. These considerations have led Florian Goertz at the Max Planck Institute for Particle and Astroparticle Physics in Heidelberg to propose the existence of a new particle that is single-handedly capable of cleaning up five of the stickiest problems in physics. “Complete symmetry is boring,” says Goertz. “If symmetry is slightly broken, interesting things can happen.” (Brooks 2018, p. 30)^[n17]

n16: Yang (1996), p. 286:

"Through the work of many physicists, the concept of broken symmetry was introduced into elementary particle physics in the 1960s and 1970s. The idea was, in the simplest language, to keep the mathematical forms symmetrical, but the physical consequence unsymmetrical. The standard model, for which Glashow, Salam, and Weinberg shared the Nobel prize in 1979, was based on gauge theory with broken symmetry. It has been extremely successful."

n17: "Physical chemistry is fundamentally asymmetric. How could it not be when the proton weighs so much more than the electron?" (Philip Stewart, pers. comm. 30 Dec 2019). A recent article along these lines appeared in New Scientist:

"Evidence of new physics could have been under our noses all along

Many of these remaining problems boil down to one. Crudely phrased, some things are exceptionally small while related things are exceptionally big. This is known as the hierarchy problem, and once you spot it, you start seeing it everywhere.

Take the four fundamental forces of nature. The weakest two are gravity, and the weak nuclear force, which only operates on the tiniest of scales and is responsible for certain types of radioactive decay. The weak force is weak, but compared with it, gravity is some 25 orders of magnitude weaker—a bizarre state of affairs that, as yet, has no good explanation.

The asymmetry reappears elsewhere. Dark energy, the mysterious force that is causing the universe’s expansion to accelerate, is 120 orders of magnitude weaker than we would expect. Dark matter, which is the dominant form of matter in the universe, interacts very weakly with regular matter. Neutrinos, the lightest particles in the standard model, are thousands of times lighter than anything else.

These disparities are profoundly vexing to physicists, who prefer to see related parameters in a theory take broadly consistent values. This preference for "naturalness" drives much theoretical speculation—some would say to a fault. 'Nature doesn't care about our aesthetics,' says [Nathaniel] Craig [a theoretical physicist at the University of California, Santa Barbara].

style="text-align:center"|* * *

Ten years on, nothing has changed. We were fixated on supersymmetry for too long, says Isabel Garcia at the University of California, Santa Barbara, searching under the convenient street light to the detriment of the field. But the story of the LHC is far from over. The collider has recorded only 3% of the data we expect it to collect in its lifetime, and an upgrade to higher energies in 2020 will further raise its chances of seeing something surprising.

But the LHC's failure to break any new ground has emboldened a new generation to question the hunches that motivated previous searches. 'This optimism is most widespread amongst the youth,' says Matthew McCullough, a theoretical physicist at CERN. 'We’ve shaken off the cobwebs of the theories handed down by our PhD advisers.'" (Eure 2019)

It remains to be seen if the YAPs (young asymmetrical pups) can teach the OSDs (old symmetrical dogs) some new tricks.

As Eugen Schwarz (2019, pers. comm., 8 Dec) stated, "The real, rich pattern of elements’ chemistry does not fit into a clear-cut rectangular grid." This view is consistent with that of Dias (2004, p. 375), who asserted that:

"A periodic table is defined as a partially ordered [italics added] set forming a two-dimensional array which complies with the triad principle where any central element has some metric property that is the arithmetic mean of two flanking [i.e. horizontal] member elements."^[n18,n19]

18: Klein (1995, pp. 341–342) elaborates the concept of a periodic table as a partially ordered set:

Even in elementary chemistry texts many "rules of thumb" are given which in effect make partial orderings of various chemico-physical properties (melting points, boiling points, electronegativities, solubilities, reactivities, etc.). For example, the ionization potentials of elements arranged in a suitable typical periodic chart generally decrease in proceeding down columns and in proceeding right-to-left across rows, so that while some pairs of elements have ionization potentials ordered by this rule, others pairs don't…Indeed, the periodic chart can be viewed as what we might call a multi-poset, where there are ordering links along both vertical and horizontal directions but orderings are to be in different directions (interchanging upward vs. downward and/or leftward vs. rightward) for various properties.

19: Even so I consider that (a) asymmetry cannot be appreciated or understood without understanding (b) symmetry, and how and why things go from (b) to (a). See also Hegstrom and Kondepudi (1990), and Rosen (1996).

Real chemists

In this vein, Mendeleev used horizontal triads when he predicted the properties of the then undiscovered elements scandium, gallium, and germanium. He discussed his technique using the horizontal triad arsenic-selenium-bromine to estimate the atomic weight of selenium (Scerri 2008, pp. 585–589).

A high degree of orderliness, and explanatory power, can nevertheless be found in Rossotti’s (1998) split d-block periodic table template (Fig. 12).

Rossotti shows where each subshell starts; how the lanthanoids and actinoids are interpositioned between Groups 2 and 4 and, in this instance, the electron configuration make-up of gadolinium and its predecessor, europium. Here, the lanthanoids run from cerium to lutetium; and the actinoids from thorium to lawrencium.

The split d-block is thus integrated into the overall design of the table.

The domain of chemistry

A related consideration is that the internal structure and external shape of a chemical periodic table is determined by chemical facts rather than considerations of regularity, beauty or symmetry (Cao et al. 2019, p. 26, passim). Here, the use of multiple considerations to triangulate a solution is consistent with the role of classification science, as well as the premise that “Classes are usually defined by more than two attributes…” (Jones 2010, p. 169). In other words, in the absence of a categorical solution we are obliged to use quantitative or qualitative arguments to establish a solution.^[n24]

24: Jones adds (2010, pp. 169–171):

"Though classification is an essential feature of all branches of science, there are always hard cases at the boundaries. The boundary of a class is rarely sharp…Scientists should not lose sleep over the hard cases. As long as a classification system is beneficial to economy of description, to structuring knowledge and to our understanding, and hard cases constitute a small minority, then keep it. If the system becomes less than useful, then scrap it and replace it with a system based on different shared characteristics."

Conclusion

It is ironic that, akin to a game of whack-a-mole, attempts to improve regularity in the appearance of the periodic table increases the number of irregularities amongst various other properties and relationships across the table, and cognitive dissonance with respect to chemical relationships between or within groups or series of elements. While Nature does not care about aesthetics, the composition of Group 3 as Sc–Y–La–Ac appears to be more consistent with the texture of the world.

That said, since periodic tables or systems form a continuum-like series of representations, different approaches to the Group 3 question (even that used within the IUAPC) will continue to have their uses. And please remember to explain the relevant context to your students.

Park 2

Electrochemistry

The following table lists standard reduction potential in volts, and electronegativity values (revised Pauling) for some metals and metalloids. Metals commonly recognised as noble metals are flagged with a ✣ symbol; metalloids are denoted ^MD; values with a † are predicted; a blank na = not available or applicable.

Element	Atomic number	Group	Period	Reaction	Poten- tial (V)	Electro- negativity	Note
Copernicium	112	12	7	Cn2+ + 2 e− → Cn	2.1		†
Roentgenium	111	11	7	Rg3+ + 3 e− → Rg	1.9		†
Darmstadtium	110	10	7	Ds2+ + 2 e− → Ds	1.7		†
Gold ✣	79	11	6	Au3+ + 3 e− → Au	1.5	2.54
Platinum ✣	78	10	6	Pt2+ + 2 e− → Pt	1.2	2.28
Iridium ✣	77	9	6	Ir3+ + 3 e− → Ir	1.16	2.2
Astatine	85	17	6	At+ + e− → At	1.0	2.2
Palladium ✣	46	10	5	Pd2+ + 2 e− → Pd	0.915	2.2
Flerovium	114	14	7	Fl2+ + 2 e− → Fl	0.9	2.21	†
Osmium ✣	76	8	6	OsO 2 + 4 H+ + 4 e− → Os + 2 H 2O	0.85	2.2
Mercury	80	12	6	Hg2+ + 2 e− → Hg	0.85	2.0
Rhodium ✣	45	9	5	Rh3+ + 3 e− → Rh	0.8	2.28
Meitnerium	109	9	7	Mt3+ + 3 e− → Mt	0.8		†
Silver ✣	47	11	5	Ag+ + e− → Ag	0.7993	1.93
Ruthenium ✣	44	8	5	Ru3+ + 3 e− → Ru	0.6	2.2
Polonium	84	16	6	Po2+ + 2 e− → Po	0.6	2.0
Nihonium	113	13	7	Nh+ + e− → Nh	0.6 †	2.09	†
Tellurium MD	52	16	5	TeO 2 + 4 H+ + 4 e− → Te + 2 H 2O	0.53	2.1
Rhenium ✣	75	7	6	Re3+ + 3 e− → Re	0.5	1.9
Water	75	7	6	H 2O + 4 e− +O 2 → 4 OH−	0.4
Hassium	108	8	7	Hs4+ + 4 e− → Hs	0.4		†
Copper	29	11	4	Cu2+ + 2 e− → Cu	0.339	2.0
Bismuth	83	15	6	Bi3+ + 3 e− → Bi	0.308	2.02
Technetium	43	7	5	Tc2+ 3 e− → Tc	0.3	1.9
Arsenic MD	33	15	4	As 4O 6 + 12 H+ + 12 e− → 4 As + 6 H 2O	0.24	2.18
Antimony MD	51	15	5	Sb 2O 3 + 6 H+ + 6 e− → 2 Sb + 3 H 2O	0.147	2.05
Bohrium	107	7	7	Bh5+ + 5 e− → Bh	0.1		†
Livermorium	116	16	7	Lv2+ + 2 e− → Lv	0.1	2.58	†

The simplified entries in the reaction column can be read in detail from the Pourbaix diagrams of the considered element in water. All elements not in this table are either not metals or have a negative standard potential.

Arsenic, antimony and tellurium are considered to be metalloids rather than noble metals.

The black tarnish commonly seen on silver arises from its sensitivity to hydrogen sulfide: 2Ag + H₂S + ½O₂ → Ag₂S + H₂O. Rayner-Canham contends that, "silver is so much more chemically-reactive and has such a different chemistry, that it should not be considered as a 'noble metal'."

The relevance of the entry for water is addressed by Li et. al. in the context of galvanic corrosion. Such a process will only occur when:

"(1) two metals which have different electrochemical potentials are…connected, (2) an aqueous phases with electrolyte exists, and (3) one of the two metals has…potential lower than the potential of the reaction (H
₂O + 4e +O
₂ = 4 OH^•) which is 0.4 V…The…metal with…a potential less than 0.4 V acts as an anode…loses electrons…and dissolves in the aqueous medium. The noble metal (with higher electrochemical potential) acts as a cathode and, under many conditions, the reaction on this electrode is generally H
₂O − 4 e^• − O
₂ = 4 OH^•)."

The superheavy elements from hassium (element 108) to livermorium (116) inclusive are expected to be "partially very noble metals"; chemical investigations of hassium has established that it behaves like its lighter congener osmium, and preliminary investigations of nihonium and flerovium have suggested but not definitively established noble behavior. Copernicium's behaviour seems to partly resemble both its lighter congener mercury and the noble gas radon.

Electronegativity is included since it is reckoned to be, "a major driver of metal nobleness and reactivity."

Status of some current categories

Alkali metals Alkaline earth metals	Most metals, by nature, are alkaline Be and Mg are endorsed by IUPAC as alkaline earth metals but neither is an "alkaline" "earth" Most of the group 3 metals; the Ln; and the late An qualify as "alkaline" "earth" metals
Transition metals	Undefined Group 12 are recognised as such on ~50/50 basis
Lanthanides	Originally defined as Ce+ IUPAC endorses La to Lu Rare earth elements is endorsed by IUPAC, and way more common than the "lanthanides" and "noble gases" terminology
Post-transition metals	Undefined Silver mostly behaves as such, rather than a TM Most popular term for metals in this part of the periodic table
Metalloids	Undefined IUPAC recommended against usage three times IUPAC recommendations widely ignored by the chemical community
Other nonmetals	No such category exists in any meaningful sense; it is a non-category The most common term for nonmetals in this part of the periodic table, across multiple disciplines, is light nonmetals
Halogen nonmetals	Named as such in recognition of their proclivity to form salts with metals esp. the AM and AEM N, O, P, S also form salts with AM and some AEM
Reactive nonmetals	Somewhat less popular than "s-block metals" Kr, Xe, and Rn are reactive nonmetals
Noble gases	Nitrogen was the original noble gas; still thought of as an inert gas

Garden

@R8R, YBG, and DePiep:

Tertiary sources. Yes, I agree these are important. So are well-known, well-defined categories.

Yes, I agree these important aspects sometimes clash, or cannot be so well-attained.

For example:

• At the very start, the boundary between metals and nonmetals is blurry.
• Halogen is a well known collective term, and the most popular of the IUPAC-endorsed names. We do not show it since it clashes with the metalloid category.
• The metalloid category is not well defined. Some authors do not recognise such a category. However, we can at least see, based on the COSMIC database (z = 194), which elements are most commonly recognised as metalloids.

Already we have to exercise some editorial pragmatism. This does not matter as long as we provide the context for doing so, and the basis for the decision.

Noble metals. Rayner-Canham (2018) recently considered how to parse the transition metals, on chemistry grounds. He surveyed the TM classification literature. His biggest sub-category was the noble metals, as PGM + gold. Silver, in comparison, is so much more chemically reactive and has such a different chemistry. Mercury is effectively not a transition metal. Once again we need to exercise some editorial pragmatism. IUPAC does not endorse noble metals as category. Nor do they endorse post-transition metals; metalloids; and reactive nonmetals. The great German text by Wiberg comments, "In place of the noble gases, the transition metal grouping has the noble metals." (2001, p. 1133).

Categories should not overlap. It’s a commendable aspiration but very many categories overlap. The overlaps are not so important. More important is that the categories provide an economy of description, a tool for structuring knowledge, and can also lead to deeper understanding.

Overlaps are solvable. We can show them using diagonal lines of demarcation, as some other authors do. The German Wikipedia has a nice table, in its lead, featuring some of these. This table has its own issues but we can do better.

Taxonomy of our scheme. Our category scheme is based primarily on metallicity and secondly on categories (not Groups):

I. Metals-metalloids-nonmetals

II. Categories.

Note the absence of a Roman-numeral-level for Groups. So the coinage metals, volatile metals, chalcogens, and pnictogens are not shown. Of course, the noble gases are shown as a category and that is fine. The noble gases are not a “Group” per se since they will not be able to accomodate oganesson, which is expected to be a solid, reactive (i.e. not noble) semiconductor (band gap 1.5 eV) having a sub-metallic appearance.

Census of periodic tables in chemistry (COPTIC database)
I looked up the taxonomical structure of periodic tables found in 62 more recent chemistry textbooks:

COPTIC results, preliminary

Taxon (% or average)	Notes (ditto, as applicable)
1. Metal-metalloid-nonmetal (35%)	Metalloid aka semiconductor; semimetal
2. Blocks (15%)	When blocks are shown, nearly all sources show all four.
3a. Categories (~50%)	Actinide; Lanthanide (67.5%) Metal (transition); Transition element; Transition metal (30%)
3b. The rest of the categories (~4.5%)	Hydrogen (~1.5%) Active metal; Light metal; Reactive metal (~5%)^ Inner transition element/metal; Metal (inner transition) (8%) Rare earth (Ln); Rare earth (Ln, An) (3%) Other metal; Poor metal; Post-transition metal (~5%) Life element; Other nonmetal (5%)
4. Groups (~10%)	Alkali earth metal; Alkali metal (8%) Alkaline earth metal (9.5%) Chalcogen (~1.5%) Halogen (11%) Noble gas (~19%)
Sundries (~3.5%)	Main group element; Representative element (~5%) Gas-liquid-solid (~3%) Nil (~3%) Main group metal; Metal (main group) (~3%)

^ Groups 1 and 2

Observations and conclusion

1. The frequency with which the Ln and An are flagged is astonishing.
2. The frequency with which Groups are not flagged is remarkable.
3. 67.5% of sources include the words lanthanides and actinides on their table.
4. Given only 10% of sources (on average) flag Groups, the field is wide open after the allocation of the categories: s-block or equivalent (~20%)§; Ln; An; TM; Metalloid; and Noble gas.
5. Post-transition metals appears to be a reasonable choice for the leftover metals between the TM and the metalloids, given the limited range of names for the metals in this part of the periodic table.
6. I'm not sure I ever understood what was "wrong" about poor metals.
7. Looking subsequently at the ngram results, "Halogen" warrants a place in some fashion, as does "Noble metal".
8. The periodic table in the lead of our periodic table article is deficient given there is no immediately accompanying colour category legend (cf the German example).

§ = s-block (15%) + Active metal; Light metal; Reactive metal (~5%) = ~20%

Nonmetal categories

"While I am eager to be proven wrong, I continue to think that there is no good divide at all. I see myself agreeing on a divide with two clear self-descriptive relevant terms, but throughout all of this time, we haven't found a single one. --R8R (talk) 17:36, 10 September 2017 (UTC)

In light of item 7 above this does indeed happen.

Light metals

"If there were a category even remotely resembling in popularity AM and AEM, we could consider it. " R8R (talk) 11:43, 11 September 2020 (UTC)

Deming included Al among the light metals, along with the group 1 and 2 metals. It’s a good category name since that is exactly what these metals are. The link between Be and Al is strong. And light metals avoids the problems with the "alkaline earth metals" name i.e. that Be and Mg are not alkaline earths. Light metals got an Ngram of 13-15; the AM and AEMs average 77. I’d say 18% is more than good enough to regarded as, at least, "remote".

Light metals is fourteen times as popular as post-transition metals and reactive nonmetals, both of which we show. The numerous properties the distinguish the halogen nonmetals from the remaining "reactive nonmetals" are set out in the literature. Here they are again:

Shared properties of H, C-O; P-S; Se

1. Sub-metallic, coloured or colourless appearance, and brittle comportment if solid	6. Multiple vertical, horizontal and diagonal relationships
2. Moderate net non-metallic character	7. Uses in combustion and explosives
3. Covalent or polymeric compounds†	8. Uses in nerve agents
4. Prominent biogeochemical roles	9. Uses in organocatalysis
5. Proclivity to catenate (form chains or rings)‡	10. Dualistic Jekyll (#4) and Hyde (#7, 8) behaviours.

† A small clarification about oxygen. Metal oxides are usually ionic. On the other hand, high valence oxides of metals, and the oxides of metalloids and nonmetals, are usually either polymeric or covalent.

‡ Since H₃⁺ is featured in interstellar chemistry this could be said to be unconvincing. Yet that is not the point. Instead, there is a spectrum of applicable properties in each category. Carbon is the most prolific catenator. Hydrogen happens to the poor cousin, that is all.

While it is essential that a periodic table displays important trends in element chemistry at ambient conditions we need to keep our eyes open for unexpected chemical behaviour in near ambient, or unusual conditions. A combination of ambient, near ambient, and unusual condition experimental data and theoretical insight supports a more nuanced understanding of complex periodic trends and non-periodic phenomena.

In ambient or near ambient conditions there is more to hydrogen:

• Theories of the structure of water involve three-dimensional networks of tetrahedra and chains and rings, linked via hydrogen bonding.
• A polycatenated network, with rings formed from metal-templated hemispheres linked by hydrogen bonds, was reported in 2008.
• In organic chemistry, hydrogen bonding is known to facilitate the formation of chain structures. C₁₀H₁₆O 4-tricyclanol, for example, shows catenated hydrogen bonding between the hydroxyl groups, leading to the formation of helical chains; crystalline isophthalic acid C₈H₆O₄ is built up from molecules connected by hydrogen bonds, forming infinite chain.
• In unusual conditions, a 1-dimensional series of hydrogen molecules confined within a single wall carbon nanotube is expected to become metallic at a relatively low pressure of 163.5 GPa. This is about 40% of the ~400 Gpa thought to be required to metallise ordinary hydrogen, a pressure which is difficult to access experimentally.

In light of these further considerations I argue that hydrogen has a not insignificant linking capacity.

Here's where this is headed; I've discussed replacing the lanthanides with the rare earth metals elsewhere:

Legend 3: Periodic table categories

Metal				Metalloid	Nonmetal
Light metal A	Rare earth metal	Transition metal (ρ, ✣)	Post-transition metal		Pre-halogen nonmetal	Halogen nonmetal	Noble gas
	Actinide

A Including aluminium

ρ Transition (rare earth) metal: Sc, Y, La

✣ Transition (noble) metal: Ru-Pd, Os-Pt, Au

Rare earth metal is there in light of its ngram popularity, and the fact that at least the label "Lanthanide series" ought to be shown on our table. That is, the lanthanide category name will be retained. R8R: I see you responded to the rare earth proposal separately; I'll follow on with a response.

YBG supports a merge of AM and AEM, as do I. R8R has expressed support for two nonmetal categories, in addition to the noble gases. I support this one too.

R8R: In terms of encyclopedia-building, all of the above more closely follows the literature than is the case now. It therefore represents an improved taxonomy.

I'll draft a better PT for the lead of our article, for you all to consider.

DePiep: Grateful for your thoughts. Sandbh (talk) 06:42, 21 September 2020 (UTC)

Colour categories

Metal					Metalloid	Nonmetal
Alkali metal	Alkaline earth metal	Lanthanoid	Transition metal	Post-transition metal		Pre-halogen nonmetal	Halogen nonmetal	Noble gas
		Actinoid	Noble metal ✣

— Colour category history 2002−2020—

2002	Rationale	ca. 2003−2013	2013−2018	2018	Proposed	Result
Alkali metal	very reactive and therefore dangerous = red	same	same	same	no change	Alkali metal
Alkaline earth metal	nice earthy colour = easy to remember					Alkaline earth metal
Lanthanoid	chosen arbitrarily					Lanthanoid
Actinoid						Actinoid
Transition metal						Transition metal
Metal	true metals are closest in colour to grey	Other metal/Poor metal	Post-transition metal			Post-transition metal
Semimetal	intermediate colour between above and below	Metalloid	same			Metalloid
Nonmetal	elements most essential to life; most life on Earth measured by biomass is photosynthetic, and chlorophyll is green	Other nonmetal	Polyatomic nonmetal (C, P−S, Se)	Reactive nonmetal	Coactive nonmetal	Coactive nonmetal
Halogen	fluorine gas is yellowish as are many precipitates of halogens	Halogen (inc. At)	Diatomic nonmetal (H, N, O, F−I)		Halogen nonmetal	Halogen nonmetal
Noble gas	non-reactive for practical purposes; light-blue is soft and soothing; aka aerogens = blue sky	same	same	same	no change	Noble gas

Clean: Group 3 and its elements in periods 6 and 7

Lanthanum and actinium (~761 words)

La and Ac below Y

Introduction

Lanthanum and actinium are commonly depicted as the remaining group 3 members.

Origin

It has been suggested that this layout originated in the 1940s, with the appearance of periodic tables relying on the ground-state electron configurations of the elements and the notion of the differentiating electron. The ground-state configurations of caesium, barium and lanthanum are [Xe]6s¹, [Xe]6s² and [Xe]5d¹6s². Lanthanum thus emerges with a 5d differentiating electron and on these grounds it was considered to be "in group 3 as the first member of the d-block for period 6". A consistent set of electron configurations is then seen in group 3: scandium [Ar]3d¹4s², yttrium [Kr]4d¹5s² and lanthanum [Xe]5d¹6s². Still in period 6, ytterbium was assigned an electron configuration of [Xe]4f¹³5d¹6s² and lutetium [Xe]4f¹⁴5d¹6s², "resulting in a 4f differentiating electron for lutetium and firmly establishing it as the last member of the f-block for period 6". Later spectroscopic work found that the electron configuration of ytterbium was in fact [Xe]4f¹⁴6s². This meant that ytterbium and lutetium—the latter with [Xe]4f¹⁴5d¹6s²—both had 14 f-electrons, "resulting in a d- rather than an f- differentiating electron" for lutetium and making it an "equally valid candidate" with [Xe]5d¹6s² lanthanum, for the group 3 periodic table position below yttrium.

Chemistry

In terms of chemical behaviour, and trends going down group 3 (if Sc-Y-La is chosen) for properties such as melting point, electronegativity and ionic radius, scandium, yttrium, lanthanum and actinium are more similar to their group 1–2 counterparts, than the other groups in the d-block.

In this variant, the number of f electrons in the most common (trivalent) ions of the f-block elements consistently matches their position in the f-block. For example, the f-electron counts for the trivalent ions of the first three f-block elements are Ce 1, Pr 2 and Nd 3.

Thorium conundrum

Lanthanum under yttrium has been criticised on the basis that it appears to create a double standard. It has been argued that La and Ac should not start the f-block as this would represent an unprecedented case of two elements in such a position with neither having electrons (f- in this case) appropriate to the block [cite L]. The double standard is said to arise since Th, with no f electron, would then start the 5f row of the f-block. If not Th, why not La and Ac? [cite J] The counterargument is that there has never been a requirement for an element to have the same differentiating electron (in this case) as its block [cite Scerri]. Thus, arguments relying on such an assumption do not shed any light on the placement question.

Split d block

This form necessitates a split d-block if expanded to a 32-column periodic table. That said, Reger, Scott and Ball (2010, p. 295) write that "perhaps" the correct shape of the 32-column periodic table should feature a split d block given the electron configurations of La and Ac, but that "we avoid these structures by splitting the f block from the rest of the periodic table. This also has the advantage of being able to print a legible periodic table on a single piece of paper." (They show La below Y in the rest of their book.) Eric Scerri considers it to be an ad hoc move that for justification requires an independent argument, that "is especially not available to authors ... who maintain that the d-block perfectly reflects the filling of five d orbitals by ten outer electrons. Why should there be a break only between the first and second of these electron-filling processes?"

Gas phase v condensed phase

Electron configurations, as commonly taught, are based on isolated atoms in a vacuum as opposed to bonded atoms in compounds, the latter being more relevant for chemistry. Moreover, for any particular atom, the lowest levels of two different configurations are often are separated by only very small energies, making which configuration happens to be the ground state chemically almost irrelevant. It is the dominant electron configuration of atoms in chemical environments, and not free gaseous atoms in a vacuum, that can rationalise qualitative chemical behaviour.

That said, the configurations associated with bonded atoms in compounds, often show different configurations.

Equally, in an Sc-Y-La-Ac table based on solid-state configurations, there are 21½ out of 28 matches with the number of f electrons in each Ln and An compared to the position of each element in the f-block, compared to 6 out of 28 for an Sc-Y-Lu-Lr table.

On this basis, solid-state electron configurations appear to support La under Y, rather than Lu.

Lutetium and lawrencium (~770 words)

Lu and Lr below Y

Introduction

In other tables, lutetium and lawrencium are the remaining group 3 members.

Origin

1920s–30s: Early techniques for chemically separating scandium, yttrium and lutetium relied on the fact that these elements occurred together in the so-called "yttrium group" whereas La and Ac occurred together in the "cerium group". Accordingly, lutetium rather than lanthanum was assigned to group 3 by some chemists in the 1920s and 30s.

1950s–60s: Several physicists in the 1950s and '60s favoured lutetium, in light of a comparison of several of its physical properties with those of lanthanum.

Electron configurations

Scandium, yttrium, and lutetium show a consistent set of electron configurations matching the global trend on the periodic table: the 5d metals then all add a closed 4f¹⁴ shell. For example, the shift from yttrium [Kr]4d¹5s² to lutetium [Xe]4f¹⁴5d¹6s² exactly parallels that from zirconium [Kr]4d²5s² to hafnium [Xe]4f¹⁴5d²6s².

Yttrium and lutetium metals have similar d-band occupancies of about 1.5 d electrons per atom; lanthanum instead has about 2.5.

The gas phase ground-state atomic electron configuration of lawrencium was confirmed in 2015 as [Rn]5f¹⁴7s²7p¹. Such a configuration represents another periodic table anomaly, regardless of whether lawrencium is located in the f-block or the d-block, as the only potentially applicable p-block position has been reserved for nihonium with its predicted configuration of [Rn]5f¹⁴6d¹⁰7s²7p¹. However, it is expected that in the condensed phase and in chemical environments lawrencium has the expected 6d occupancy, and simple modelling studies suggest it will behave like a lanthanide, in particular being a homologue of lutetium.

In this variant, the number of f electrons in the gaseous forms of the f-block atoms usually matches their position in the f-block. For example, the f-electron counts for the first five f-block elements are La 0, Ce 1, Pr 3, Nd 4 and Pm 5.

Chemistry (inc. periodic trends)

Vertical trends

Trends going down group 3 (if Sc-Y-Lu is chosen) for properties such as melting point, electronegativity and ionic radius, are similar to those found among their group 4–8 counterparts in the same block, as noted by Jensen in an often-cited 1982 article in which he argued for this placement.

In this variant, the number of f electrons in the gaseous forms of the f-block atoms usually matches their position in the f-block. For example, the f-electron counts for the first five f-block elements are La 0, Ce 1, Pr 3, Nd 4 and Pm 5.

Horizontal trends

Lawrencium's return to +3 as the only stable oxidation state and being predicted to form a trivalent metal is distinct from the behaviour of the other late actinides fermium, mendelevium, and nobelium, which have a tendency towards forming lower oxidation states and form (or are predicted to form) divalent metals; it also makes an exception to the actinide contraction generally being larger than the analogous lanthanide contraction at the end of both series. The steadily increasing stability of the +2 state along the actinide series going to nobelium is similar to that along the 3d series going to zinc.

The inclusion of lutetium rather than lanthanum also homogenises the 5d transition series: trends in atomic size, coordination number, and relative abundance of metal–oxygen bonds all reveal that lutetium is closer than lanthanum to the behaviour of the uncontroversial 5d metals hafnium through mercury. The same is true considering conduction band structures of the elements: lutetium has a transition-metal-like conduction band structure, but lanthanum does not.

General

While scandium, yttrium and lutetium (and lawrencium, so far as its chemistry is known) do often behave like trivalent versions of the group 1–2 metals, being hard class-A cations mostly restricted to the group oxidation state, they are not the only elements in the d-block or f-block that do so. The early transition metals zirconium and hafnium in group 4, as well as niobium and tantalum in group 5, also display such behaviour, as does the actinide thorium. (The heavy group 4 elements and thorium are tetravalent; the heavy group 5 elements are pentavalent.)

Separation groups

The phenomenon of different separation groups is caused by increasing basicity with increasing radius, and does not constitute a fundamental reason to show Lu, rather than La, below Y. Thus, among the Group 2 alkaline earth metals, Mg (less basic) belongs in the "soluble group" and Ca, Sr and Ba (more basic) occur in the "ammonium carbonate group". Nevertheless, Mg, Ca, Sr and Ba are routinely collocated in Group 2 of the periodic table.

Lack of 4f electron

This arrangement, in which lanthanum is the first member of the f-block, is disputed by some authors since lanthanum lacks any f-electrons.

Commented: Group 3 and its elements in periods 6 and 7

Lanthanum and actinium

La and Ac below Y

Support

Introduction

Lanthanum and actinium are commonly depicted as the remaining group 3 members.

Origin

It has been suggested that this layout originated in the 1940s, with the appearance of periodic tables relying on the ground-state electron configurations of the elements and the notion of the differentiating electron. The ground-state configurations of caesium, barium and lanthanum are [Xe]6s¹, [Xe]6s² and [Xe]5d¹6s². Lanthanum thus emerges with a 5d differentiating electron and on these grounds it was considered to be "in group 3 as the first member of the d-block for period 6". A consistent set of electron configurations is then seen in group 3: scandium [Ar]3d¹4s², yttrium [Kr]4d¹5s² and lanthanum [Xe]5d¹6s². Still in period 6, ytterbium was assigned an electron configuration of [Xe]4f¹³5d¹6s² and lutetium [Xe]4f¹⁴5d¹6s², "resulting in a 4f differentiating electron for lutetium and firmly establishing it as the last member of the f-block for period 6". Later spectroscopic work found that the electron configuration of ytterbium was in fact [Xe]4f¹⁴6s². This meant that ytterbium and lutetium—the latter with [Xe]4f¹⁴5d¹6s²—both had 14 f-electrons, "resulting in a d- rather than an f- differentiating electron" for lutetium and making it an "equally valid candidate" with [Xe]5d¹6s² lanthanum, for the group 3 periodic table position below yttrium.

Commentary (for review)

However, many elements do not have a well-defined single differentiating electron from the previous element when considering ground-state gas-phase electron configurations; for example, the ground-state configuration of vanadium is [Ar]3d34s2, and that of chromium is [Ar]3d54s1, in which two d electrons are added and one s electron is removed. Lanthanum has the advantage of incumbency since the 5d1 electron appears for the first time in its structure whereas it appears for the third time in lutetium, having also made a brief second appearance in gadolinium. However, the same may be said of thorium which has incumbency over rutherfordium for the 6d2 position; yet rutherfordium is universally placed there.

Chemistry

In terms of chemical behaviour, and trends going down group 3 (if Sc-Y-La is chosen) for properties such as melting point, electronegativity and ionic radius, scandium, yttrium, lanthanum and actinium are more similar to their group 1–2 counterparts, than the other groups in the d-block.

Commentary (not for draft)
I dispute this. I believe it should read "Sc, Y, La, Ac are similar to their group 1-2 counterparts. However, they are not the only elements to show such similarities: so do the heavy group 4 and 5 elements." We may discuss these similarities first, of course. Double sharp (talk) 08:09, 26 May 2020 (UTC)

In this variant, the number of f electrons in the most common (trivalent) ions of the f-block elements consistently matches their position in the f-block. For example, the f-electron counts for the trivalent ions of the first three f-block elements are Ce 1, Pr 2 and Nd 3.

Notes for consideration)
[Notes] IUPAC survey? Goncharova & Il'ina? Lavelle? Reger, Scott and Ball Restrepo? Scerri, on d/e; Shchukarev; Shriver & Atkins; Spedding and Beadry? Success of electron configuration as first obtained from spectroscopy, noting this field primarily deals with gas phase atoms; Ternstrom; d occupancy of La = dhcp structure?

Commentary (not for draft)

The last does not work. La without f involvement would be hcp, as Sc, Y, Lu, Lr indeed are, but La is not (per Wittig). Not to mention that Y and Lu have ~1.5 d electrons per atom, and according to Pettifor La has ~2.5. I also note that Pettifor says Zr also has ~2.5, yet it is somehow not dhcp. Pettifor claims hybridisation, but Hamilton notes that dhcp seems to only appear in the f elements. Besides, Pettifor in his later book Bonding and Structure of Molecules and Solids already notes that the part of the transition metal trend where hybridisation is needed to get the right structures are the late transition metals (group 10), and notes that the trend of structures for nonmagnetic transition metals "is driven by the d bond contribution alone" (p. 223). So La still ends up looking mysterious as usual, whereas Lu smoothly continues the trend as expected (same for Ac vs Lr). Actually, most of these have either already been dealt with by the exposure of the irrelevance of ground-state gas-phase configurations below, or by Jensen's call for intraperiod as well as intragroup analogies. The few topics in chemistry that require focusing on gas-phase configurations certainly do not form a significant majority. Double sharp (talk) 03:24, 25 May 2020 (UTC)

More commentary (not for draft)

Lavelle's "pair out of place" argument, in which he writes "However placing lanthanum (La) and actinium (Ac) in the f-block is the only case where a pair4 of elements that belong in the same group are systematically placed in a group that results in their being part of a block with no outer electrons in common with that block." has two serious problems: (1) The exact same thing is true if you put lutetium (Lu) and lawrencium (Lr) in the f-block. Neither has outer f electrons, those f electrons are never used for chemistry. (2) Lavelle's only argument for why thorium shouldn't be treated like actinium (neither have an f-electron) is because thorium's lighter congener is cerium, which does have the required f electron. Which suggests that once element 122 is discovered (only four elements away), and if the calculations are right that it lacks the requisite g-electron in the ground state, then we cannot tell whether it is supposed to go in the g-block until we discover its heavier congener and see if it has a g-electron. Because if eka-122 doesn't have a g electron, then it's a "pair out of place", but if it does, then it's just the reverse of the Ce-Th situation. I think this is obviously undesirable: the placement of an element should clearly be established from its own properties. Double sharp (talk) 04:54, 26 May 2020 (UTC)

Oppose

Thorium conundrum

Lanthanum under yttrium has been criticised on the basis that it appears to create a double standard. It has been argued that La and Ac should not start the f-block as this would represent an unprecedented case of two elements in such a position with neither having electrons (f- in this case) appropriate to the block [cite L]. The double standard is said to arise since Th, with no f electron, would then start the 5f row of the f-block. If not Th, why not La and Ac? [cite J] The counterargument is that there has never been a requirement for an element to have the same differentiating electron (in this case) as its block [cite Scerri]. Thus, arguments relying on such an assumption do not shed any light on the placement question.

Commentary (not for draft)

As noted in the commentary I think this is not an accurate summary of the arguments. I propose the following instead: Double sharp (talk) 08:15, 26 May 2020 (UTC) The form with lanthanum under yttrium has been defended on the grounds that lanthanum and actinium in their ground-state configurations (respectively [Xe]5d16s2 and [Rn]6d17s2) have no electrons in f subshells and therefore should not be placed in the f-block. However, this creates an inconsistency in the treatment of thorium, which has no f-electrons in the ground-state (being [Rn]6d27s2), similar to actinium as [Rn]6d17s2; yet it places thorium in the f-block but not actinium. Considering only ground-state gas-phase configurations, thorium [Rn]6d27s2 by itself is just as good a homologue to zirconium [Kr]4d25s2 as lanthanum [Xe]5d16s2 is to scandium [Ar]3d14s2; yet thorium is invariably placed in the f-block, not in group 4 with zirconium. Thorium thus demonstrates that the possession of an f electron in the ground-state gas-phase configuration of an element is not necessary for it to belong to the f-block. Lanthanum and actinium in a Sc-Y-Lu table do form the only paired anomaly where both elements in a group have no outer electrons in their ground-state gas-phase configurations that match their block. However, the same is true for lutetium and lawrencium in a Sc-Y-La table, neither of which are known in states beyond +3 and for which the f orbitals are definitely core orbitals. This is still not exactly the double standard. Starting the row was not Jensen's and Scerri's point. It was just that Ac [Rn]5f06d17s2 and Th [Rn]5f06d27s2 are being treated inconsistently: one is allowed into the f-block despite having no f electrons in the ground-state gas-phase configuration, the other is not. What Scerri is furthermore saying is that having f electrons in the ground-state gas-phase configuration, not having an f "differentiating electron" (which he did not refer to), is not actually relevant to whether an element gets to go into the f block. Jensen similarly points to ideal Madelung configurations, which also implies agreement with Scerri's point. And that is why they both refer to thorium: differentiating electrons have nothing to do with it. I attach the quotes below for easy reference. Double sharp (talk) 09:19, 25 May 2020 (UTC) “ In his commentary, Lavelle argues that the above reasoning is outdated based on recent calculations that suggest that Lr does not have an outer (n – 1)d1ns2 valence configuration but rather a ns2np1 valence configuration, thus placing it in the p-block as a heavier analog of Tl. I must confess that this was news to me as I am sure it was to most of the readers of this Journal. As a chemist I do not feel qualified to pass judgement on how seriously one should take such results, but I do know if the results are correct, then they seriously undermine our current understanding of the periodic table. Furthermore, I also know that one cannot consistently argue that these results negate the placement of Lr in the d-block and then turn around, as Lavelle does in ref 1, Note 1, and argue that they can be blithely ignored when it comes to assigning Lr to the f-block! Similarly, it is inconsistent for Lavelle to dismiss (ref 1, Note 4) the (n – 1)d2 ns2 valence configuration of Th as an inconvenient irregularity that should not affect its assignment to the f-block as an idealized (n – 2)f2 ns2 element and then turn around and insist that it is absolutely verboten to entertain the idea that La and Ac may have similar irregular valence configurations corresponding to an idealized (n – 2)f1 ns2 valence configuration. After all both elements have low-lying empty f orbitals, which is more than can be said for Lu and Lr. Indeed, more than a quarter of the elements in the d- and f-blocks have irregular valence configurations and in several instances these irregularities apply to the majority of the elements within a given group. The simple fact is that the periodic table is based on idealized electronic configurations rather than on actual configurations and in this fashion functions in chemistry much as the ideal gas law or the concepts of ideal crystals and ideal solutions. ” — Jensen “ However, there is no requirement that every block of the periodic table must necessarily consist of atoms that contain exactly the number and type of electrons predicted from the combination of quantum numbers that are obtained from solving the Schrödinger equation for a one-electron system. For example, much theoretical work has been conducted into which element will feature the first appearance of a g electron. Although there is some debate about this question there is unanimous agreement among theoreticians that it will not take place at element 121 as one might expect on simplistic grounds. The first few elements in what will be termed the g-block will probably not contain a g electron (7)! Better still, consider the configuration of thorium, [Rn]6d27s2. This element follows actinium, and nobody disputes placing it in the f-block even though it does not possesses any outer f electrons. The possession of an outer f electron is clearly not a requirement for an element to be placed in the, nominally named, f-block. ” — Scerri That is not at all why Sc-Y-La is criticised. Sc-Y-Lu places more elements without f electrons in ground-state gas-phase configurations into the f-block. Sc-Y-La is criticised, e.g. by Jensen, because it creates a double standard. Ac and Th are treated differently by it. Double sharp (talk) 05:18, 25 May 2020 (UTC) [Notes]: Jensen does not argue this in the cite. He said it was hypocritical of L to dismiss Th as an inconvenience and to then not entertain La and Ac on the same grounds. But that is not an argument L ever raised. His point was having two elements each having no f electron in the ground state at the start of the f block would be unprecedented. I accept that these are two different arguments, and we may certainly add Lavelle's argument separately. It is, I note, already addressed by other matters (i.e. that gas-phase configurations don't matter and the 4f collapse starts at La anyway). Double sharp (talk) 06:25, 25 May 2020 (UTC) Jorgensen is only stating the obvious. He did not add, "yet thorium is invariably placed in the f-block, not in group 4 with zirconium." No, he did not indeed. But you can see that in pretty much all periodic tables published since Seaborg. I am not opposed to removing the addition, but even if it is removed the conclusion it represents pretty obviously jumps out at the reader. Double sharp (talk) 06:25, 25 May 2020 (UTC)

Split d block

This form necessitates a split d-block if expanded to a 32-column periodic table. That said, Reger, Scott and Ball (2010, p. 295) write that "perhaps" the correct shape of the 32-column periodic table should feature a split d block given the electron configurations of La and Ac, but that "we avoid these structures by splitting the f block from the rest of the periodic table. This also has the advantage of being able to print a legible periodic table on a single piece of paper." (They show La below Y in the rest of their book.) Eric Scerri considers it to be an ad hoc move that for justification requires an independent argument, that "is especially not available to authors ... who maintain that the d-block perfectly reflects the filling of five d orbitals by ten outer electrons. Why should there be a break only between the first and second of these electron-filling processes?"

Gas phase v condensed phase

Electron configurations, as commonly taught, are based on isolated atoms in a vacuum as opposed to bonded atoms in compounds, the latter being more relevant for chemistry. Moreover, for any particular atom, the lowest levels of two different configurations are often are separated by only very small energies, making which configuration happens to be the ground state chemically almost irrelevant. It is the dominant electron configuration of atoms in chemical environments, and not free gaseous atoms in a vacuum, that can rationalise qualitative chemical behaviour.

Note + Commentary (not for draft)

[Note]: Where is this going? It is going to the point that La has 4f involvement. Unfortunately, due to the organisation into La-Ac and Lu-Lr sections it is difficult to accomplish this without some repetition... Double sharp (talk) 08:13, 26 May 2020 (UTC) The point of this is that ground-state electron configurations don't mean very much at all for chemistry and therefore they are not a particularly strong argument against putting La in the f-block. I suppose it should say something here, rather than below, about lanthanum's 4f involvement in chemical environments, viz. its occupancy in compounds and its collapsing at La. Which is stronger than that of any other lanthanide. Double sharp (talk) 09:25, 25 May 2020 (UTC)

That said, the configurations associated with bonded atoms in compounds, often show different configurations.

Equally, in an Sc-Y-La-Ac table based on solid-state configurations, there are 21½ out of 28 matches with the number of f electrons in each Ln and An compared to the position of each element in the f-block, compared to 6 out of 28 for an Sc-Y-Lu-Lr table.

On this basis, solid-state electron configurations appear to support La under Y, rather than Lu.

Commentary (not for draft)

Disputed by me, see below. Double sharp (talk) 08:16, 26 May 2020 (UTC) What do you think the solid-state configurations of the Ln are? There isn't any integer occupancy here, so there's literally speaking 0 matches with anything. Just a mix of various configurations with localised and delocalised 4f electrons and therefore with fluctuating f electron counts. That incidentally gives the right understanding of the 4fn to 4f(n-1) motif. You just have to consider averages, which will contain for La configurations with a 4f electron in the conduction band (that's what the non-integers mean), but never for Lu. Double sharp (talk) 09:16, 25 May 2020 (UTC) [Note] Gas phase consistent; condensed phase variable Gas phase consistent and irrelevant, condensed phase varying according to the compound and respecting real chemistry. Double sharp (talk) 05:17, 25 May 2020 (UTC) @Double sharp: Configurations were first obtained from spectroscopy and this field primarily deals with gas phase atoms. Following on, Jensen (2009, Misapplying the periodic law) said: "The simple fact is that the periodic table is based on idealized electronic configurations rather than on actual configurations and in this fashion functions in chemistry much as the ideal gas law or the concepts of ideal crystals and ideal solutions." I get that. Why then are there no such things as idealised solid state configurations to teach instead? Sandbh (talk) 06:53, 25 May 2020 (UTC) It is not too hard to create such things. Either follow the Madelung rule as if it had no exceptions (and in some sense it doesn't because the "right" configurations are always within a few eV anyway), e.g. Cr = [Ar]3d44s2, or go for my "fuzzy configurations" like La = [Xe] (4f5d6s6p)3 that is similar to how authors talk about (sd)3 band metals. The first one is exactly what Jensen is obviously referring to in his response to Lavelle. I suppose you don't see them much explicitly only because gas-phase configurations usually get put in this role instead, even though their irregularities from the Madelung rule don't have much in the way of chemical relevance. Double sharp (talk) 07:09, 25 May 2020 (UTC)

Lutetium and lawrencium

Lu and Lr below Y

Support

Introduction

In other tables, lutetium and lawrencium are the remaining group 3 members.

Origin

1920s–30s: Early techniques for chemically separating scandium, yttrium and lutetium relied on the fact that these elements occurred together in the so-called "yttrium group" whereas La and Ac occurred together in the "cerium group". Accordingly, lutetium rather than lanthanum was assigned to group 3 by some chemists in the 1920s and 30s.

1950s–60s: Several physicists in the 1950s and '60s favoured lutetium, in light of a comparison of several of its physical properties with those of lanthanum.

Physical properties elaborated)
d-electron presence The physical properties of the group 3 elements are affected by the presence of a d electron, which forms more localised bonds within the metals than the p electrons in the similar group 13 metals; exactly the same situation is found comparing group 4 to group 14.

Commentary (not for draft)
[Note] As is the case for La The point of this was to show that physically speaking, group 3 is absolutely a d-block group, and should follow d-block trends. Double sharp (talk) 05:12, 25 May 2020 (UTC)

Crystal structure

Crystal structures of the d elements (‡ = distorted)

Sc	Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn
hcp	hcp	bcc	bcc	α-Mn	bcc	hcp	fcc	fcc	hcp‡
Y	Zr	Nb	Mo	Tc	Ru	Rh	Pd	Ag	Cd
hcp	hcp	bcc	bcc	hcp	hcp	fcc	fcc	fcc	fcc‡
Lu	Hf	Ta	W	Re	Os	Ir	Pt	Au	Hg
hcp	hcp	bcc	bcc	hcp	hcp	fcc	fcc	fcc	rhm
Lr	Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Cn
hcp	hcp	bcc	bcc	hcp	hcp	fcc	bcc	bcc	bcc

Most of the transition metals, including lutetium, have normal, close-packed, crystalline strutures except for manganese and mercury. Zinc and cadmium show distorted structures associated with being closer to the metal-nonmetal dividing line. With the exception of the strongly relativistic late 6d elements and the magnetic middle 3d elements, crystal structure varies completely regularly with valence. This is observed with Lu in group 3, but not with La in group 3: La is dhcp, Ac is fcc.

Melting point

schneidner, analysing the melting points of the lanthanides, concluded it was likely that 4f, 5d, 6s, and 6p electrons were all involved in the bonding of lanthanide metals except for lutetium. 4f electrons have been invoked to explain the low melting point of lanthanum metal (La 920 °C, versus Sc 1541 °C, Y 1526 °C, Lu 1652 °C)) The fact that lanthanum was demonstrated to be a 4f-band metal (with about 0.17 electrons per atom in fcc lanthanum, which is metastable at standard conditions) whereas the 4f shell appears to have no influence on the metallic properties of lutetium, has been used as an argument to place lutetium in group 3 instead of lanthanum.

It was noted, for example, that since the 4f sub-shell was complete in Lu it should be placed in the d-block [cite L & L].

4f electron influence in La: Lanthanum has low-lying non-hydrogenic empty f orbitals, which lutetium lacks. These orbitals contribute measurably to the bonding in some lanthanum compounds, for example in lanthanum(III) fluoride (LaF₃). While this contribution is small, it is greater for lanthanum than for any other lanthanide. Meanwhile, the Lu–F 4f–2p bond order in LuF₃ is less than the analogous one of IrF₃, with iridium well into the 5d block.

Commentary (not for draft)

[Eh?]: The order of involvement of 4f in lanthanum is as minor as that of 5f in thorium; that of 4f in cerium is at least as important as that of 5f in uranium. Point being, that (1) 4f collapses faster than 5f; (2) and therefore thorium has about as strong f involvement as lanthanum, and so the spectre of the double standard gets raised again if you allow one in the f-block but not the other on the grounds of f involvement. Double sharp (talk) 09:19, 25 May 2020 (UTC)

Electron configurations

Scandium, yttrium, and lutetium show a consistent set of electron configurations matching the global trend on the periodic table: the 5d metals then all add a closed 4f¹⁴ shell. For example, the shift from yttrium [Kr]4d¹5s² to lutetium [Xe]4f¹⁴5d¹6s² exactly parallels that from zirconium [Kr]4d²5s² to hafnium [Xe]4f¹⁴5d²6s².

Yttrium and lutetium metals have similar d-band occupancies of about 1.5 d electrons per atom; lanthanum instead has about 2.5.

The gas phase ground-state atomic electron configuration of lawrencium was confirmed in 2015 as [Rn]5f¹⁴7s²7p¹. Such a configuration represents another periodic table anomaly, regardless of whether lawrencium is located in the f-block or the d-block, as the only potentially applicable p-block position has been reserved for nihonium with its predicted configuration of [Rn]5f¹⁴6d¹⁰7s²7p¹. However, it is expected that in the condensed phase and in chemical environments lawrencium has the expected 6d occupancy, and simple modelling studies suggest it will behave like a lanthanide, in particular being a homologue of lutetium.

In this variant, the number of f electrons in the gaseous forms of the f-block atoms usually matches their position in the f-block. For example, the f-electron counts for the first five f-block elements are La 0, Ce 1, Pr 3, Nd 4 and Pm 5.

Chemistry (inc. periodic trends)

Vertical trends

Trends going down group 3 (if Sc-Y-Lu is chosen) for properties such as melting point, electronegativity and ionic radius, are similar to those found among their group 4–8 counterparts in the same block, as noted by Jensen in an often-cited 1982 article in which he argued for this placement.

In this variant, the number of f electrons in the gaseous forms of the f-block atoms usually matches their position in the f-block. For example, the f-electron counts for the first five f-block elements are La 0, Ce 1, Pr 3, Nd 4 and Pm 5.

Horizontal trends

Lawrencium's return to +3 as the only stable oxidation state and being predicted to form a trivalent metal is distinct from the behaviour of the other late actinides fermium, mendelevium, and nobelium, which have a tendency towards forming lower oxidation states and form (or are predicted to form) divalent metals; it also makes an exception to the actinide contraction generally being larger than the analogous lanthanide contraction at the end of both series. The steadily increasing stability of the +2 state along the actinide series going to nobelium is similar to that along the 3d series going to zinc.

The inclusion of lutetium rather than lanthanum also homogenises the 5d transition series: trends in atomic size, coordination number, and relative abundance of metal–oxygen bonds all reveal that lutetium is closer than lanthanum to the behaviour of the uncontroversial 5d metals hafnium through mercury. The same is true considering conduction band structures of the elements: lutetium has a transition-metal-like conduction band structure, but lanthanum does not.

General

While scandium, yttrium and lutetium (and lawrencium, so far as its chemistry is known) do often behave like trivalent versions of the group 1–2 metals, being hard class-A cations mostly restricted to the group oxidation state, they are not the only elements in the d-block or f-block that do so. The early transition metals zirconium and hafnium in group 4, as well as niobium and tantalum in group 5, also display such behaviour, as does the actinide thorium. (The heavy group 4 elements and thorium are tetravalent; the heavy group 5 elements are pentavalent.)

Notes for consideration)
[Notes] Jensen too selective; Zr-Hf have no aqueous chemistry other than in abnormal conditions; Nb, Ti = very little aqueous chemistry: C&W pp. 882, 887; +4 is too high to be ionic (G&E, p. 958).

Commentary (not for draft)

Group Cation % area pH range 1 +1 80 −1 to 15 2 +2 57 −1 to 15 3 (Sc-Ac) +3 36 −1 to 4–7¾ 3 (Ce-Lu) +3 35 −1 to 5½–7 4 (Ti) +2 4.7 −1 to 4 4 (Ti) +3 0.3 −1 to 1 4 (Ti) +4 nil n/a 4 (Zr, Hf) +any nil n/a 5 (V) +2 4.9 −1 to 7 5 (V) +3 1.7 −1 to 2¾ 5 (Nb, Ta) +any nil n/a 6 (Cr) +2 2.5 −1 to 6 6 (Cr) +3 6.0 −1 to 4 6 (Mo) +3 0.5 −1 to 1 6 (W) +any nil n/a 7 (Mn) +2 11 −1 to 8 7 (Tc) +any nil n/a 7 (Re) +3 0.4 −1 to 1 That's not true, as even if Zr4+ and Hf4+ need low pH (which is a criterion that will exclude the tetravalent actinides) there are still going to be moderately hydrolysed species at normal pH above 0 like ZrO2+ and HfO2+ (see Marcel Pourbaix's Atlas of Electrochemical Equilibria in Aqueous Solutions). As for +4 supposedly being too high to be ionic, just look at the high melting point of HfO2 (cite: Wulfsberg again). As usual this is just a matter of how electronegative the counter-anion is. Cationic species of Nb and Ta in water are indeed hard to find, but for sure both elements show a variety of anionic species in alkaline solutions as Greenwood and Earnshaw note. Greenwood and Earnshaw agree that heavy group 4 and 5 are mostly restricted to the group oxidation state and are class-A elements. I don't disagree that we have to report that Jensen has been accused of being too selective. But to back that up we will need to quote some trends that are supposed to favour Sc-Y-La. Double sharp (talk) 16:54, 24 May 2020 (UTC) In my sandbox please refrain from expressions such as "completely false". It's a question of how to present this information in a balanced, contextual manner. C&W write, "Aqueous chemistry: This is not very extensive because a +4 ion, even a large one, tends to be extensively hydrolysed. Only at very low concentration (~10−4 M) and high acidity ([H+] of 1–2 M) does the Zr4+ (aq) ion appear to exist…No ZrO2+ ion has been detected convincingly. Instead there seems to be a more or less direct conversion of Zr4+ (aq) to tetranuclear [Zr4(OH)8(H2O16]8+ and octanuclear [Zr8(OH)20(H20O)24]12+ species…[Nb and Ta] have very little cationic behaviour. Schweitzer and Porterfield (The aqueous chemistry of the elements, 2010), give E-pH diagrams covering pH –1 to 15, and E(V) −4 to 3. The table shows how much area each group's cations (aq) occupy in their diagrams. There is a good contrast between groups 1 to 3, and 4+. The pH ranges for An(IV) are Th: −1 to 3; Pa: −1 to 0; U: −1 to −0.5; Np: −1 to 0.5; Pu −1 to 0; Bk −1 to 4.5. In the context of S&P, the An are not excluded, whereas Zr-Hf, and Nb-Ta are. Sandbh (talk) 04:30, 25 May 2020 (UTC) Fine, changed to "not true". Just look at Pourbaix and you will see predominance regions for Zr4+ below 0.5, Hf4+ below about -0.7. Of course MO2+ are just stoichiometries and you will have lots of other hydrolysed species. That is not in any sense different from the behaviour of Be or Al. There is still no contrast, only a continuum as the needed acidity goes up from +1 cations to +2 cations to +3 cations to +4 cations. Also, you see exactly the same difference passing from group 13 to group 14, actually even worse because Ge4+, Sn4+, and Pb4+ can't persist in water at any pH, which at the very least proves that this is not a sufficient reason by itself to split a block. Double sharp (talk) 05:15, 25 May 2020 (UTC)

Notes for consideration)

[Notes] Further, the choice of electronegativity scale is a little arbitrary. The Pauling scale, for example, favours Sc-Y-La. Groups 1, 2, 4, and 5 have the period 6 element somewhat more electropositive than the period 5 element; this works with La (1.1) under Y (1.22) but not with Lu (1.27) under Y. In the Mulliken scale (Boeyens 2008, pp. 207–208), the values for La (1.74) and Lu (1.70) are both less than that of Y (1.81).

Oppose

Separation groups

The phenomenon of different separation groups is caused by increasing basicity with increasing radius, and does not constitute a fundamental reason to show Lu, rather than La, below Y. Thus, among the Group 2 alkaline earth metals, Mg (less basic) belongs in the "soluble group" and Ca, Sr and Ba (more basic) occur in the "ammonium carbonate group". Nevertheless, Mg, Ca, Sr and Ba are routinely collocated in Group 2 of the periodic table.

Commentary (not for draft)

Quite apart from the fact that "increasing basicity with increasing radius" is not the full story (as Wulfsberg notes, the most electronegative metals have in fact an acidity that belies their size, just look at BiIII as an obvious example), it also depends on the whole idea that radius must increase down the table, which Jørgensen already addressed. Already Zr-Hf and Nb-Ta are not increases. Why should there be one below Y? Double sharp (talk) 16:57, 24 May 2020 (UTC)

Lack of 4f electron

This arrangement, in which lanthanum is the first member of the f-block, is disputed by some authors since lanthanum lacks any f-electrons.

Commentary (not for draft)
This is a repetition of a La argument, which has been dealt with by pointing to (1) the irrelevance of ground-state gas-phase configurations and (2) the double standard of thorium. Double sharp (talk) 05:19, 25 May 2020 (UTC)

First sweep progress line:

---

THE REST OF THE SANDBOX

Classifying the elements (C)

The progression from metallic to nonmetallic character in traversing the periodic table shows a pleasing symmetry

Active metals Groups 1–3, Ln, An, (Al)			Corrosive nonmetals O, F, Cl, Br, I
Transition metals Most of groups 4–11			Related nonmetals H, C, N, P, S, Se
Poor metals (Al), Ga, Bi etc			Metalloids (weak nonmetals) B, Si, Ge, As, Sb, Te
Noble metals Ru, Rh, Pd, Ag, Os, Ir, Pt, Au			Noble gases He, Ne, Ar, Kr, Xe, Rn

Notes
1. The category name related nonmetals is analogous to older references to the transition metals as related metals, for example:

• Ebel IL 1938, "Atomic structure and the periodic table", Journal of Chemical Education, vol. 15, no. 12, p. 575
• Quagliano JV & Vallarino LM 1969, Chemistry, Prentice-Hall, 3rd ed., Englewood Cliffs, NJ, p. 848
• Luder WF 1970, "The atomic structure chart of the elements," Canadian Chemical Education, April, p. 13

That is a pleasing coincidence i.e. that the transition metals line up with the related nonmetals.

2. The related nonmetals are related by the H-C-P-N-S-Se thread.

3. I'm eschewing the term post-transition metal so as to not have to deal with the question of Al, or perhaps I should move it into the active metals category?

4. I was inspired to revisit the symmetry and names of these eight categories by:

• Scerri ER 2012, "A critique of Wiesberg's view on the periodic table and some speculations on the nature of classifications", Foundations of Chemistry, vol. 14, no. 3, pp. 275–284.

5. Praise be that all category names are relatively short.

6. The balanced 6-6-5-6 distribution of the nonmetals is pleasing.

7. An article to follow, in an appropriate publication. Sandbh (talk) 04:38, 7 September 2019 (UTC)

Antimony as a metalloid

I've been wondering why, from a literature perspective, antimony came to be included among the elements commonly recognised as metalloids.

I suspect there are various "memes" involved. A meme is an idea, behaviour, or style that spreads from person to person within a culture. Here they are, in rough historical order:

0. Pliny the Elder made a distinction between "male" and "female" forms of antimony; the male form was probably the sulfide, while the female form, which is superior, heavier, and less friable, has been suspected to be native antimony.

1. Bastardry. Arsenic, antimony, and bismuth were historically called bastard metals or semimetals on account of their brittle nature. As well, metals were supposed to be fusible. The fact that arsenic sublimed rather than melted further sullied its reputation.

2. Allotropy. Antimony, like arsenic, was known in "metallic" and non-metallic forms. Tin escaped this meme because it was malleable. An equivalent non-metallic allotrope of bismuth was not known.

3. Mendeleev described tellurium as forming a transition between metals and nonmetals. Curiously, he referred to As and Sb as metals, and to Bi as a perfect [sic] metal. That got the hares running as to which other elements could be regarded as forming a transition between metals and nonmetals.

4.  Semiconductivity. Johan Koenigsberger classified solid materials as metals, insulators and "variable conductors" in 1914 although his student Josef Weiss already introduced the term Halbleiter (semiconductor in modern meaning) in his PhD thesis of 1910. The subsequent development of semiconductor physics sparked a renewed interest in Ge and Si, and to a lesser extent, B, as halfway elements. As well, the elements to either side of Sb namely Sn and Te existed in semiconducting forms (noting that grey tin behaves like a semiconductor but is actually a semimetal) so it was expected that Sb would also exist in a semiconducting form, which it did (Moss 1952, p. 173).

5. Metalloid line. Deming's 1923 periodic table made it easier to make out a notional dividing line between metals and nonmetals, naturally focusing attention on the elements to either side namely Be and B; Al and Si; Ge and As; Sb and Te; and Po and At. Note the absence of Bi.

6. Amphoterism. The amphoteric character of:

• Ge and As, lying as they do between Ga (a metal) and Se (usually considered to be a nonmetal; and
• Sb and Te, lying as they do between Sn (a metal) and I (a nonmetal),

came to be associated with a transition in metallic character, from metallic to nonmetallic.

The situation in period 6 was less clear. The sequence of elements involved is Pb Bi, Po, and At. Lead is a metal. Astatine was popularly thought to be a halogen, and therefore a nonmetal (although the folks who first synthesised it thought it was a metal). On this basis it could’ve been thought that Bi and Po would be amphoteric. However Bi was regarded as basic, and only Po showed some amphoteric character, which may have resulted in some authors regarding it as a metalloid.

7. Pauling published his influential book General chemistry (1947) in which he referred to B, Si, Ge, As, Sb, Te, and Po as being metalloids. (He erroneously referred to Sb as being a semiconductor.)

8. Rochow published The metalloids (1966) and recognised B, Si, Ge, As, Sb, and Te as such.

9. Group 15. The progression in metallic character going down group 15 tended to reinforce regarding Bi as a metal, but not Sb. For example:

• "Antimony…is more nonmetallic than metallic…bismuth…more nearly approaches a metal in physical and chemical properties." (Norris & Young 1938, p. 529)
• "The trisulphides of arsenic and antimony are acidic, forming salts with yellow ammonium sulphide and alkali, while that of bismuth is typical of a metal." (Moody 1969, pp. 267, 321)
• "All the elements react readily with halogens but are unaffected by non-oxidising acids. Nitric acid gives, respectively, phosphoric acid, arsenic acid, antimony trioxide, and bismuth nitrate, which well illustrates the increasing metallic character as the group is descended." (Cotton & Wilkinson 1976, p. 288)
• "The paucity of [stereochemical] information about Bi is due to the more metallic character of this element, which does not form many of the simple covalent molecules formed by As and Sb." (Wells 1984, p. 878)
• "Bismuth(III) oxide occurs naturally as bismite and is formed when Bi combines with O₂ on heating. In contrast to earlier members of group 15, molecular species are not observed for Bi₂O₃ and the structure is more like that of a typical metal oxide." (Housecroft & Sharpe 2008, p. 474)

I guess Sb came to be regarded as a metalloid mainly due to its brittle comportment; existence of a non-metallic semiconducting allotrope; proximity to the metalloid line; perceived amphoterism; and apparent lack of genuine salts. In contrast, Bi had only one of these features.

References

• Cotton FA & Wilkinson G 1976, Basic inorganic chemistry, Wiley, New York
  
• Housecroft CE & Sharpe AG 2008, Inorganic chemistry, 3rd ed., Pearson, Harlow
  
• Moody B 1969, Comparative inorganic chemistry, 2nd ed., Edward Arnold, London
  
• Moss TS 1952, Photoconductivity in the elements, Butterworths Scientific Publications, London
  
• Norris JF & Young RC 1938, A textbook of inorganic chemistry for colleges, 2nd ed., McGraw-Hill, New York
  
• Wells AF 1984, Structural inorganic chemistry, 5th ed., Oxford University, Oxford.

-- Sandbh (talk) 10:14, 24 May 2018 (UTC)

Table

Property	Metalloid	Chemically active nonmetal	Noble gas
Appearance	metallic	metallic, coloured, or translucent	translucent
Atomic structure	close-packed* or polyatomic	polyatomic or diatomic	monatomic
Bulk coordination number	12*, 6, 4, 3, or 2	3, 2, or 1	0
Electrical conductivity	moderate	poor to moderate	poor
Electronic structure	metallic* to semiconductor	semimetallic, semiconductor, or insulator	insulator
Ionization energy	low	moderate to high	high to very high
Electron affinity	low to high	moderate to high (exception: N is negative)	negative
Electronegativity	moderate	moderate to high	moderate to very high
Oxidising power	low (exception: At is moderate)	low to high	n/a
Compounds with metals	tend to form alloys or inter-metallic compounds	mainly covalent: H†, C, N, P, S, Se mainly ionic: O, F, Cl, Br, I	none form simple compounds

*Bulk astatine has been predicted to have a face-centred cubic structure
† Hydrogen can also form alloy-like hydrides

Response to DePiep

@DePiep: I haven’t replied so far as I’ve been stumped for an answer. I proceed with the greatest of trepidation in submitting the following thoughts.

The marvelous variety and infinite subtlety of the non-metallic elements, their compounds, structures and reactions, is not sufficiently acknowledged in the current teaching of chemistry.

JJ Zuckerman and FC Nachod
In Steudel's Chemistry of the non-metals (1977, preface)

In trying to understand the nonmetals I think there are seven perspectives to consider:

(1)	The general properties of nonmetals at standard conditions e.g. volatility, low elasticity, good insulators, they gain or share electrons when they react with other elements or compounds.
(2)	Their structures, nonmetals having a low number of nearest neighbours compared to metals.
(3)	Which of their properties are surpassed by some metals e.g. the ionisation energy of Hg exceeds that of S and I; the electronegativity of Au exceeds that of P; the electron afinity of Cd is less than than that of N.
(4)	Their anomalies e.g. H’s uniqueness; N’s low electron affinity and relative inertness, P4’s reactivity; Xe’s relatively low ionisation energy; first row v second row differences.
(5)	The chemistry of the nonmetals by group.
(6)	Patterns and trends among the nonmetals in ionisation energy, electron affinity, electronegativity and oxidising power.
(7)	Cross-cutting relationships.

I think if you can keep all this in your head than you can follow why the nonmetals are as diverse as they are. The current nonmetal article only largely does (1) and (2). The rewrite adds some of (4) and (5); a little of (6); and (7). A further rewrite would add or expand (3); (4); (5); and (6).

I tend to think a further rewrite might best be done by having only two formal categories of nonmetal: the top-shelf nonmetal category for H, C, N, P, O, S, Se, F, Cl, Br and I; and a single noble gas subcategory (noting the metalloids are similarly in a top-shelf category and have no subcategory).

The nonmetal article might go partly like this:

Nonmetals are H, C, N, P, O, S, Se in group 1 or groups 13–16; F, Cl, Br, and I in group 17; and the noble gases He, Ne, Ar, Kr, Xe and Rn in group 18. For convenience within this article, nonmetals other than the noble gases are hereafter referred to using the descriptive phrase "chemically active nonmetals"; and the four group 17 elements are referred to as "halogen nonmetals". Of these terms only "noble gases" and "halogen" are IUPAC-approved.

The chemically active nonmetals have a diverse range of individual physical and chemical properties. In periodic table terms they largely occupy a position between the weakly nonmetallic metalloids to the left and the noble gases to the right.

Physically, four are solids, one is a liquid (bromine), and six are gases. Of the solids, carbon, selenium, and iodine are metallic-looking, whereas sulfur has a pale-yellow appearance. Ordinary white phosphorus has a yellowish-white appearance but the black allotrope, which is the most stable form of phosphorus, has a metallic-looking appearance. Bromine is reddish-brown in colour. Of the gases, fluorine and chlorine are coloured pale yellow, and yellowish green. Electrically, most are insulators whereas carbon is a semimetal and black phosphorus, selenium and iodine are semiconductors.

Chemically, they tend to have higher ionisation energies, electron affinities, and electronegativity values, and be relatively strong oxidising agents, in comparison to metals. Collectively, the highest values of these properties are found among oxygen and the halogen nonmetals. Manifestations of this status include oxygen's major association with the ubiquitous processes of corrosion and combustion, and the intrinsically corrosive nature of the halogen nonmetals. All five of these nonmetals exhibit a tendency to form predominately ionic compounds with metals whereas the remaining nonmetals tend to form predominately covalent compounds with metals.

Characteristic and other properties of metalloids, chemically active nonmetals, and noble gases are summarised in the following table. Metalloids have been included in light of their generally nonmetallic chemistry. Physical properties are listed in loose order of ease of determination; chemical properties run from general to specific, and then to descriptive. While the table shows the main points of difference it is somewhat arbitrary since exceptions and boundary overlaps can be found within each category. Important instances of these are so noted.

In writing this it occurs to me that such an approach might work just as well for the di/polyatomic/noble gases. So, after all that, I still don’t know which one will work best. At least you know I haven’t stopped thinking about this/working on it.

I presume project members would be happy with either outcome, depending on how the article in question looked. Whatever the outcome my intention is to have a better, more lucid nonmetal article. It may be that I'll have to do both rewrites.

Somewhere, if we do not do so already, we perhaps need to say that:

(1)	our categorisation scheme is not definitive;
(2)	for convenience and economy of description we… (a) use IUPAC-approved collective names for the alkali metals, alkaline earth metals, and noble gases; (b) do not use the IUPAC-approved collective names lanthanoids, actinoids, rare earth metals, pnictogens, and chalcogens; (c) refer to the leftover elements as either post-transition metals, or metalloids, or "nonmetals" for nonmetals not categorised as noble gases i.e. H, C, N, P, O, S, Se and the halogen nonmetals (akin to the LANL periodic table);
(3)	there is a spectrum of properties within each category;
(4)	it is not hard to find overlaps at the boundaries, as is the case with most classification schemes.

And perhaps these caveats need to be flagged some more in the periodic table article. Sandbh (talk) 08:45, 5 October 2017 (UTC)

RfC

I am seeking comments on a proposal to change part of the current nonmetal categorisation scheme, as follows:

From	Polyatomic nonmetal C, P, S, Se	Diatomic nonmetal H, N, O, F, Cl, Br, I
To	Less active nonmetal H, C, N, P, S, Se	Active nonmetal O, F, Cl, Br, I

Origin
The origin of this proposal can be traced to literature conceptions of nonmetals as either halogens (F, Cl, Br, I, At), noble gases, or other metals (H, C, N, O, P, S, Se), with the last of these three groupings representing a poorly characterised "orphan" or leftovers category.

The Wikipedia periodic table used to show the three categories of halogens, noble gases, and other nonmetals up until we recategorised astatine as a metalloid. Astatine has been predicted to have a metallic crystalline structure, which suggests there may be grounds to categorise it as a post-transition metal. But condensed astatine has not yet been observed so for the moment is left as a metalloid.

When astatine was recategorised as metalloid the opportunity was taken to get rid of the nondescript "other nonmetal" category name by moving C, P, S, and Se into a new polyatomic nonmetal category, and moving H, N, and O, into a new diatomic nonmetal category, along with F, Cl, Br, and I.

You can see this current arrangement, which is based on structural considerations, in the nonmetal article. It works, but I've never been completely satisfied with it since it does not necessarily show the most relevant trends associated with nonmetallic character. Chemists tend to think of nonmetals primarily in terms of such things as oxidative power, electronegativity, activity, reactivity, anionic behaviour, or electron affinity, rather than whether the nonmetals have polyatomic or diatomic molecular structures.

Proposal
In retrospect I think it would better to categorise H, C, N, P, S, and Se as less active nonmetals, and O, F, Cl, Br, and I as active nonmetals. Such a division would be based on multiple electrochemical properties, rather than a single structural consideration.

In this arrangement, O, F, Cl, Br, and I are individually and collectively characterised by relatively high ionisation energies, high electronegativities, high electron affinities, high oxidising power, and simple anion formation, consistent with their depiction in the literature.

H, C, N, P, S and Se are unable to consistently match the active nonmetals across the aforementioned electrochemical properties.

The proposed category names, which end with the form "-ive", can accommodate the fact that, for example, while the overall tendency of H and S is to act as reducing agents, they are sometimes capable of acting as oxidants. Another example would be the fact that nitrogen has a higher electronegativity than bromine and iodine. Now nitrogen does show some "active" character in its capacity to form hydrogen bonds and complexes, but it is a poor oxidising agent unless combined with an active nonmetal like O or F; and it is a reluctant anion former, unlike the active nonmetals. So, at the broadbush level being dealt with here, N is a less active nonmetal, with some "active" nuances if you dig deeper. This is consistent with the meaning of the "-ive" suffix: "that performs or tends toward or serves to accomplish an indicated action esp. regularly or lastingly" or "having a tendency to, having the nature, character, or quality of, given to (some action)". Hence it has the meaning of a tendency rather than a finality.

On the question of boundary overlaps such as these I turn also to Jones (2010, pp. 169–171):

"Classes are usually defined by more than two attributes…Though classification is an essential feature of all branches of science, there are always hard cases at the boundaries. The boundary of a class is rarely sharp…Scientists should not lose sleep over the hard cases. As long as a classification system is beneficial to economy of description, to structuring knowledge and to our understanding, and hard cases constitute a small minority, then keep it. If the system becomes less than useful, then scrap it and replace it with a system based on different shared characteristics."

Similar overlaps occur elsewhere in the periodic table. For example, beryllium in group 2, an alkaline earth metal, behaves chemically more like aluminium in group 3, a post-transition metal; the group 3 transition metals scandium, yttrium, lanthanum and actinium behave largely like the alkaline earth metals or, more generally, s block metals; and gallium in group 13, tin in group 14, and bismuth in group 15, all of which are post-transition metals, have some metalloid properties.

The periodic table nevertheless retains its status as an organising icon of chemistry.

What does IUPAC say?
IUPAC does not provide any guidance on category names for the nonmetals. They have endorsed use of the terms "noble gases" and "halogens" however these are group names rather than category names such as post-transition metal, and metalloid, neither of which are IUPAC endorsed. We do show the group names in our larger periodic table, but we don't have a halogen colour category since we count astatine as a metalloid, which has a different colour category.

What's the go with "halogens" and "other nonmetals"?
As I mentioned, the literature largely distinguishes between noble gases, halogens, and "the rest of the nonmetals". Categorising astatine as a metalloid mitigates against the use of the "halogens" category. The term other nonmetal is occasionally used however this is not based on any consideration of the shared attributes that should characterise a useful category name. And it's an awkward term to use if you want to say something like, for example, "nonmetals form compounds with metals and other nonmetals" or "like hydrogen, carbon forms molecular covalent compounds with most other nonmetals."

What does the literature say?
As it turns out, there is support in the literature for the terms "less active nonmetal", and "active nonmetal". Here are some quotes that use this terminology and highlight the distinctiveness of O, F, Cl, Br, and I.

• "A salt is a compound of metal ions and nonmetal ions. The halogens being active nonmetals are excellent salt-formers." (Allen et al. 1942, p. 484)
• "What, in general, is the difference between active metals, less active metals, less active non-metals, active non-metals, and inert gases…?" (Friedenberg 1946, p. 230)
• "Most commonly metals and halogens form ionic solids." (Pearson & Mawby, 1956, p. 55)
• "The halogens and oxygen are the most active non-metals." (Lee & Van Orden 1965, p. 197)
• "The most active non-metals are in the upper right-hand corner of the chart; the most active metals are in the lower left-hand corner." (Luder 1965, p. 39)
• "From Group V on, the series passes from the less active nonmetals to the most active ones, like chlorine, in Group Vll." (Gardiner & Flemister 1967, p. 22)
• "Across each period is a more or less steady transition from an active metal through less active metals and weakly active non-metals to highly active nonmetals and finally to an inert gas." (Beiser 1968, p. 234)
• "If you don't count the noble gases, Family 18, the most active non-metals are found in the upper right corner." (Aldridge 1993, p. 175)
• "Active nonmetals, such as the halogens (Group VIIA) and oxygen, are good oxidizing agents." (Grolier Incorporated 1999, p. 162)
• "Oxygen is one of the most active nonmetals and one of the most important. It forms compounds with all the elements except the light noble gases (He, Ne, and Ar). In general, oxygen forms ionic compounds with metals…" (Hill and Petrucci 1999, p. 903)

What the new scheme would look like
A draft rewrite of the nonmetal article using the proposed descriptive category names of less active nonmetal and active nonmetal can be found here.

The proposed scheme would result is a more balanced distribution of nonmetals, from 4 + 7, to 6 + 5.

It is the culmination of around five months of discussion with members of WikiProject Elements. Along the way we considered but discarded a range of alternative paired category names, including: weak/strong; intermediate/corrosive; reactive/corrosive; reductive/corrosive; covalent/ionic, heterogenic/corrosive; foundation/corrosive; formative/corrosive; and less active/corrosive.

Summary
I propose to replace the diatomic and polyatomic nonmetal categories with the newly constituted categories of less active nonmetal, and active nonmetal, as sourced from the literature. These categories are more consistent with the most relevant trends associated with nonmetallic character.

References

• Aldridge B et al. 1993, Science interactions, Glencoe/McGraw-Hill, New York
• Allen JS, French SJ, Woodruff JG 1942, Atoms, rocks and galaxies: a survey in physical science, Harper and Brothers, New York
  
• Beiser A 1968, Perspectives of modern physics, McGraw-Hill, New York
• Friedenberg EZ 1946, A Technique for developing courses in physical science adapted to the needs of students at the junior college level, University of Chicago, Chicago
• Gardiner MS & Flemister SC 1967, The principles of general biology, Macmillan, New York
• Grollier Incorporated 1999, The encyclopaedia Americana, vol. 21, Danbury, Connecticut
• Hill JW & Petrucci RH 1999, General chemistry: An integrated approach, Prentice Hall, Upper Saddle River, New Jersey
• Jones BW 2010, Pluto: Sentinel of the outer Solar System, Cambridge University Press, Cambridge
• Lee GL & Van Orden HO 1965, General chemistry: Inorganic and organic, 2nd ed., Saunders, Philadelphia
• Luder WF 1965, General chemistry, Saunders, Philadelphia
• Pearson RG & Mawby RJ 1967, "The nature of metal–halogen bonds", in V Gutmann (ed.), Halogen chemistry, Academic Press, London

-- Sandbh (talk) 03:29, 9 September 2017 (UTC)

Nonmetal boxes

Nonmetal (EN)	EN span*	EA
He (5.5)		−50
Ne (4.84)		−120
F (3.98)		328
O (3.44)		141
Cl (3.16), Ar (3.2)	0.04	349, –96
N (3.04)		−0.07
Br (2.96), Kr (2.94)		325, −60
I (2.66)		295
C (2.55), S (2.58), Se (2.55)	0.03	122, 200, 195
Xe (2.4)		–80
H (2.2), P (2.19), As (2.18), At (2.2)	0.01–0.02	73, 72, 78, 222
Te (2.1), Rn (2.06)	0.04	190, −70
B (2.04), Ge (2.01), Sb (2.05)	0.03–0.04	27, 119, 101
Si (1.9)		134

* Pauling's EN values had an uncertainty of ±0.05

Nonmetal redraft

Is here.

Parsing the nonmetals

Abstract

In this essay the nonmetals are described in terms of what is generally well-known about them, and how they are summarised in the literature. Specific aspects of their nonmetallic character are then highlighted, namely oxidative power, electronegativity, activity, reactivity, anionic behaviour, and electron affinity. On the basis of a high degree of correlation among these properties, there is an evident trichotomy among the nonmetals.

The view from the top

1.  From the literature we know that:

• nonmetals, at the outset, are characterised by a lack of metallic properties;
• the alkali metals and the halogens provide the most distinct contrast between metals and nonmetals;
• the most reactive metals are found towards the bottom left of the PT, and the most reactive nonmetals are found in the upper right hand corner just inside the noble gases; and that
• apart from the halogens, and the noble gases, there are the remaining nonmetals.

2.  The noble gases will not further be considered.

3.  This quote then provides an overview of the nonmetals under consideration:

The behaviour of the nonmetals can be summarised as follows. Nonmetals tend to oxidize metals…Nonmetals with relatively large electronegativities (such as oxygen and chlorine) oxidise substances with which they react…Nonmetals with relatively small electronegativities (such as carbon and hydrogen) can reduce other substances…Oxygen is the perfect example of an oxidizing agent because it increases the oxidation state almost any substance with which it reacts (p. 9)…The chemistry of the halogens is dominated by oxidation-reduction reactions (p. 35).

– Bodner, Rickard & Spencer 1996, module 1 pp. 3, 9, 35

Table 1: NONMETAL CLASSES

Electronegativity
High	O, F, Cl, Br, I
Moderate	C, N, S, Se
Weak	H, P

Table 2: NONMETAL CLASSES

Strongly electronegative	O, F
Moderately electronegative	Br, Cl
Weakly electronegative	C, N, S, I
Approximately electro-neutral	B, H, P
Weakly electro-positive	Si

Table 3: AVERAGE E⁰ FOR NONMETALS,
STABLE SPECIES, pH 0, –3.0 to 3.0 V

Strong	Fluorine: F2 + 2e → 2HF = 2.87 Oxygen: O3 + 2e → O2 = 2.08; O2 + 4e → 2H2O = 1.23; then (2.08 + 1.23)/2 = 1.65 Bromine: BrO4– + 2e → BrO3– = 1.85; 2BrO3– + 10e → Br2 = 1.48; Br2 → 2Br– + 2e = 1.07; then (1.85 + 1.48 + 1.07)/3 = 1.46 Chlorine: 2ClO4– + 14e → Cl2 = 1.38; Cl2 + 2e → 2Cl– = 1.36; then (1.38 + 1.36)/2 = 1.37 Iodine: H5IO6 + 2e → IO3– = 1.6; 2IO3– + 10e → I2 = 1.19; I2 +2e → 2I– = 0.53; then (1.6 + 1.19 + 0.53)/3 = 1.1
Moderate	Sulfur: S2O8–2 → 2HSO4– = 2.06; HSO4– + 6e → S = 0.39; S + 2e → H2S = 0.14; then (2.06 + 0.39 + 0.14)/3 = 0.86 Nitrogen: 2NO3– → N2 = 1.25; N2 + 6e → 2NH4– = 0.27; then (1.25 + 0.27)/2 = 0.76 Selenium: HSeO4– → H2SeO3 = 1.15; H2SeO3 + 4e → Se = 0.74; Se + 2e → H2Se = –0.11; then (1.15 + 0.74 – 0.11)/3 = 0.59
Weak	Tellurium: H6TeO6 + 2e → TeO2 = 0.93; TeO2 + 4e → Te = 0.57; Te + 2e → H2Te = –0.69; then (0.93 + 0.57 – 0.69)/3 = 0.27 Arsenic: H3AsO4 + 2e → As4O6 = 0.56; As4O6 + 12e → As = 0.24; As + 3e → AsH3 = –0.22; then (0.56 + 0.24 – 0.22/3) = 0.19 Carbon: CO2 + 4e → C = 0.21; C + 4e → CH4 = 0.13; then (0.21 + 0.13)/2 = 0.17 Antimony: Sb2O5 + 2e → Sb2O3 = 0.70; Sb2O3 + 6e → Sb = 0.15; Sb + 3e → SbH3 = –0.51; then (0.70 + 0.15 – 0.51)/3 = 0.11
	Phosphorus: H3PO4 → PH3 = –0.28 Germanium: GeO2 + 4e → Ge = –0.25; Ge + 4e → GeH4 = –0.87; then (–0.25 – 0.87)/2 = –0.56 Boron: B(OH)3 + 3e → B = –0.89 Silicon: SiO2 + 4e → Si = –0.91 Hydrogen: 2H+ + 2e → H2 = 0.0; H2 + 2e → 2H– = –2.25; then (0.0 – 2.25)/2 = –1.12
Wulfsberg 2000, pp. 247–249, 273–276 Schweitzer 2010, pp. 228–229, 232–233

Table 4: NONMETAL PROPERTIES

Nonmetal	Ionisation energy (kJ/mol)	Electron affinity (eV)	Electro-negativity
B	897	27	2.04
Si	793	134	1.9
Ge	768	119	2.01
As	953	79	2.18
Sb	840	101	2.05
Te	879	190	2.1
At	899	233	2.2
H	1,318	73	2.2
C	1,093	122	2.55
N	1,407	−0.07	3.04
P	1,018	72	2.19
S	1,006	200	2.58
Se	947	195	2.55
O	1,320	141	3.44
F	1,687	328	3.98
Cl	1,257	349	3.16
Br	1,146	324	2.96
I	1,015	295	2.66
He	2,372	−50	5.5
Ne	2,088	−120	4.84
Ar	1,521	−96	3.2
Kr	1,351	−60	2.94
Xe	1,170	−80	2.4
Rn	1,037	−70	2.06

Cross-cutting themes

4.  We can compare the former approach (that of Bodner et al.) with the nonmetal groupings of Synder (1966, p. 242) in Table 1, and Nelson (2011, p. 55) in Table 2. The latter author wisely writes (p. 57):

In using [the table]…care needs to be taken to remember that it is only an approximation, and can only be used as a rough guide to the properties of the elements. Provided that this is done, however, it constitutes a very useful classification, and although purists often despise it because of its approximate nature, the fact is that practising chemists make a great deal of use of it, if only subconsciously, in thinking of the chemistry of different elements.

5.  We can consider the nonmetal displacement series of (a) Parkes & Mellor (1943, p. 205), and (b) Ashford (1967, p. 312), and observe a similar pattern:

(a) F…O…Cl…Br…I…S…P…Se…N…C

(b) F…Cl…O…Br…I…S…N

6.  On the relationship between an element and its compounds Jones (1973, p. 159) writes that:

It is usual when discussing the factors which contribute to the overall chemistry of an element to consider the fundamental atomic properties. Such properties fall broadly into two groups: (1) properties of the free…atom itself which can be measure or calculated directly, e.g., atomic weight or ionisation energy, and (2) properties associated with concepts used to rationalise the behaviour of the…atom in chemically combined states, such as electro-negativity and electron affinity.

7.  In this context, average standard reduction potentials for the elements and their stable species in aqueous solution (table 3) correlate well with the observations of all of these authors. Note that while nitrogen itself has a high electronegativity it is a poor oxidising agent. And only when it is in a positive oxidation state (i.e. in combination with oxygen or fluorine) are its compounds good oxidising agents (Cox 2004, p. 161). The latter author thus writes that "Nitrogen is a moderately electronegative element…" In contrast, oxygen and the halogens are relatively strong oxidising agents (Rudolph 1974, p. 133).

8.  Consistent with table 3, and in discussing the redox behaviour of the elements, Silberberg (2006, p. 548), in a periodic table extract, shows only O, F, Cl, Br, and I as strong oxidising agents.

9.  The theme of distinguishing O, F, Cl, Br and I from the other nonmetals is further reinforced by the literature:

(a) "The halogens and oxygen are the most active non-metals." (Lee & Van Orden 1965, p. 197)

(b) "…under SSIMS [secondary ion mass spectrometry] conditions…the electronegative elements, i.e. oxygen, fluorine, chlorine, bromine and iodine, give intense negative ion signals." (Briggs 1998, p. 119)

(c) "Simple anionic chemistry is limited to oxygen and the halogens, although polyanions and polycations can be formed by many [nonmetals]." (Cox 2004, p. 145)

(d) "For chemists…the most important feature of an element is its pattern of chemical behaviour, in particular, its tendency toward covalent bond formation (or its preference for cation formation)." (Rayner-Canham & Overton 2006, p. 29)

(e) "Of the nonmetals, oxygen and the halogens are highly reactive." (Frank, Miller & Little 2004, p. 19)

(f) "A few nonmetallic elements, such as oxygen and the halogens (F₂, Cl₂, Br₂, and I₂) are strong oxidizing agents…" (Moore & Stanitski 2015, p. 114)

10.  More generally, the higher an element's ionisation energy, electron affinity, and electronegativity, the more nonmetallic that element is (Yonder, Suydam & Snavely 1975, p. 58). Table 4 shows that O, F, Cl, Br and I collectively have the highest values of these properties among the nonmetals.

Boundary overlaps

11.  Notwithstanding the shared characteristics of oxygen and the halogen nonmetals, some of these are evident in the remaining nonmetals such as nitrogen with its high ionisation energy and electronegativity, and sulfur which has an ionisation energy near that of iodine, and a high electron affinity.

12.  On the question of boundary overlaps such as these I turn to Jones (2010, pp. 169–171):

"Classes are usually defined by more than two attributes…Though classification is an essential feature of all branches of science, there are always hard cases at the boundaries. The boundary of a class is rarely sharp…Scientists should not lose sleep over the hard cases. As long as a classification system is beneficial to economy of description, to structuring knowledge and to our understanding, and hard cases constitute a small minority, then keep it. If the system becomes less than useful, then scrap it and replace it with a system based on different shared characteristics."

13.  Similar overlaps occur elsewhere in the periodic table. For example, beryllium in group 2, an alkaline earth metal behaves chemically more like aluminium in group 3, a post-transition metal; the group 3 transition metals scandium, yttrium, lanthanum and actinium behave largely like the alkaline earth metals or, more generally, s block metals; and gallium in group 13, tin in group 14, and bismuth in group 15, all of which are post-transition metals, have some metalloid properties.

14.  The periodic table nevertheless retains its status as an organising icon of chemistry.

15.  On the specific question of nitrogen we can see that, like oxygen, its high electronegativity manifests in its ability to form relatively strong hydrogen bonds, its capacity to enter into coordination complexes, and a preference for multiple bonding over catenation.

16.  Unlike oxygen, we can see that nitrogen is reluctant to form simple anions, hence nearly all of its compounds are covalent, that it is a poor oxidising agent, and that the metal nitrides resemble in many ways, the borides, carbides, and phosphides.

17.  On the basis of the relative importance of anion formation, covalent bonding, and oxidising power, I concur with the distinction made in the literature between (a) oxygen and the halogen nonmetals as being more nonmetallic than (b) nitrogen, and the assignment of the latter, on an overall basis, to a moderately or weakly electronegative nonmetal category, on par with the treatment of e.g. carbon or sulfur.

18.  On the specific question of sulfur I rely on a comparison with iodine, and note that iodine:

• has a significantly higher electron affinity, and a higher electronegativity rating, and a marginally higher ionisation energy;
• is a stronger oxidizing agent, by itself, and on average;
• occurs before sulfur in various nonmetal displacement series;
• is most stable in an oxidation state of –1 compared to the +6 of sulfur; and
• generally resembles the other halogen nonmetals in its chemical properties.

19.  While nitrogen and sulfur share some characteristics with oxygen and the halogens these similarities are either selective or of a relatively second order nature. Neither element exhibits a sufficiently effective preponderance of headland nonmetallic properties.

The remaining nonmetals

20.  These are the metalloids B, Si, Ge, As, Sb, Te, and At, and the other nonmetals H, C, N, P, S, and Se. The metalloids are counted here in view of their generally nonmetallic chemistry. The properties of the remaining nonmetals are summarised in Table 5. Oxygen and the halogen nonmetals are included for comparative purposes. Physical properties are listed in loose order of ease of determination; chemical properties run from general to specific, and then to descriptive.

TABLE 5: PROPERTIES OF METALLOIDS, OTHER NONMETALS, AND OXYGEN AND THE HALOGEN NONMETALS

Physical property	Metalloids	Other nonmetals	O and the halogen nonmetals
Form	solid	mainly solid	mainly gaseous
Appearance	lustrous	lustrous to colourless	mainly coloured
Bulk coordination number	2–6	1–3	1
Allotropes	most form allotropes		O forms an allotrope
Electrical conductivity	intermediate	poor to intermediate	poor
Electronic structure	semimetal to semiconductor	semimetal to insulator	semiconductor to insulator
Outer s and p electrons	3–7	1, 4–6	6–7
Crystal structure	rhombohedral: B, As, Sb cubic: Si, Ge, At? hexagonal: Te orthorhombic: At	cubic: P hexagonal: H, C, N, Se orthorhombic: S	cubic: O, F   orthorhombic: Cl, Br, I
Atomic radius, calculated, (pm)	mainly more than 100 (87–133)	mainly less than 100 (42–115)
Packing efficiency (%)	• 34–41 • 28 for astatine	17–28.5	23.9 for iodine
Chemical property	Metalloids	Other nonmetals	O and the halogen nonmetals
General chemical behaviour	nonmetallic
Ionization energy	low	low to high	high to very high
Electron affinity (kJ/mol)	low to high (27–233)	• mainly moderate to high (72–200) • N is slightly negative (–1.4)	high (141–349)
Electronegativity	moderate	moderate to high	high
Oxidizing power	low	low to moderate	high
Oxidation states	negative and positive known for all	• negative and positive known for all • negative is unstable for H	• negative known for all • positive known for all but F, and only exceptionally for O
Compounds with metals	can form alloys	mainly covalent	mainly ionic
Compounds with carbon	carbides and organometallic compounds	carbon-nonmetal (e.g. CS2, CCl4) or organic (e.g. CH4, C6H12O6) compounds
Oxides	• amphoteric or weakly acidic • polymeric in structure • glass formers (B, Si, Ge, As, Sb, Te)	• neutral to strongly acidic • molecular covalent • few glass formers (P, S, Se) • H2O can form a glass at ~136 K or −137 °C; CO2 does so at 40 GPa	• strongly acidic • iodine oxides known in polymeric forms • no known glass formers
Sulfates	most form	some form	iodine forms
Conventional hydrogen bond formation	not known	known for S and N	known for O, F, Cl, and Br

21.  A distinction can be seen between (a) oxygen and the halogens and (b) the other nonmetals, in terms of the most important properties that characterise nonmetals, namely oxidising power and covalent v ionic bonding tendencies. This distinction is correlated with differences in ionisation energy, electron affinity, and electronegativity.

22.  A comparable distinction can be made between the other nonmetals and the metalloids, consistent with increasing metallic character in proceeding back from the noble gases. In this sense, the metalloids represent the most metallic of the nonmetals. If they were any more metallic they would likely be classed as metals, rather than occupying the eastern half of the periodic table's frontier territory, the western half being occupied by post-transition metals.

23.  It is pertinent to note that, just as the metalloids cluster along a diagonal path, similar diagonal relationships occur among the other nonmetals between carbon and phosphorus, and between nitrogen and sulfur; and amidst oxygen and the halogen nonmetals, between oxygen and chlorine.

24.  As flagged, the divides between the three categories of nonmetals, in terms of receding metallicity, are not absolute. Boundary overlaps occur as outlying elements in each category show (or begin to show) less-distinct, hybrid-like or atypical properties.

25.  They nevertheless provide a useful way of organising and structuring what is known about the nonmetals, consistent with literature-based conceptions of more active and less active nonmetals, and the generally nonmetallic chemistry of the metalloids.

Nomenclature

26.  Oxygen and the halogens are hereafter referred to as "corrosive nonmetals", oxygen by its association with the ubiquitous processes of corrosion and combustion, both of which are forms of oxidation (itself a paronym of oxygen); and the halogen nonmetals by virtue of their intrinsically corrosive nature.

27.  The remaining nonmetals are hereafter referred to as "intermediate nonmetals" in light of their intermediate nonmetallic character, and periodic table location between the metalloids and the corrosive nonmetals.

Conclusion

Literature-based conceptions of the nonmetals and their electro-active properties show a high degree of correlation. The most nonmetallic of the nonmetals are O, F, Cl, Br, and I. They are individually and collectively characterised by high ionisation energy, high electronegativity, high electron affinity, high oxidising power, and simple anion formation. "Though by no means all identical, their similarities sufficiently outweigh their differences" such that it is conceptually and didactically convenient to group O, F, Cl, Br, and I under the rubric of corrosive nonmetals, "as an approximate expression of all of them." (Nelson 2011, p. 55) The metalloids are characterised as the most metallic of the nonmetals. The other nonmetals are neither as metallic as the metalloids to the left nor as nonmetallic as the corrosive nonmetals to the right and, accordingly, are most appropriately conceived of as intermediate nonmetals.

References

• Ashford TA 1967, The physical sciences, 2nd ed., Holt, Reinhart and Winston, New York
  
• Bodner GM, Rickard LH, Spencer JN 1996, Chemistry: structure and dynamics, John Wiley & Sons, Chichester
  
• Briggs D 1998, Surface analysis of polymers by XPS and static SIMS, Cambridge University Press, Cambridge
• Cox PA 2004, Inorganic chemistry, 2nd ed., BIOS Scientific Publishers, London
• Frank DV, Miller S & Little JG 2004, Prentice Hall Science Explorer: Chemical Interactions, 3rd ed., Prentice Hall, Upper Saddle River, New Jersey
• Jones K 1973, "Nitrogen", in JC Bailar et al., Comprehensive inorganic chemistry, vol. 2, Pergamon Press, Oxford
• Jones BW 2010, Pluto: Sentinel of the outer Solar System, Cambridge University Press, Cambridge
• Lee GL & Van Orden HO 1965, General chemistry: Inorganic and organic, 2nd ed., Saunders, Philadelphia
• Moore JW & Stanitski CL 2015, Chemistry: The molecular science, 5th ed., Cengage Learning, Australia
• Nelson PG 2011, Introduction to inorganic chemistry: Key ideas and their experimental basis, Ventus Publishing ApS. Self-published but Nelson is a published chemist in peer reviewed journals and "often writes on matters of conceptual chemistry" Scerri (1996, p. 174).
• Parkes GD & Mellor JW 1943, Mellor's modern inorganic chemistry, Longmans, Green and Co., London
  
• Rayner-Canham G & Overton T 2006, Descriptive inorganic chemistry, 4th ed., WH Freeman and Company, New York
• Rudolph J 1974, Chemistry for the modern mind, Macmillan, New York: "…oxygen and the halogens in particular…are therefore strong oxidizing agents."
• Scerri ER 1996, "Stephen Brush, the Periodic Table and the nature of chemistry," Die Sprache der Chemie, P Jannich, N Psarros (eds), Könighausen & Neumann, Würzburg, pp. 169–176 (171)
• Schweitzer GK & Pesterfield LL 2010, The aqueous chemistry of the elements, Oxford University Press, Oxford
• Silberberg MS 2006, Chemistry: The molecular nature of matter and change, 4th ed., McGraw-Hill, Boston
• Synder MK 1966, Chemistry: Structure and reactions, Holt, Rinehart and Winston, New York
• Wulfsberg G 2000, Inorganic chemistry, University Science Books, Sausalito, California
• Yoder CH, Suydam FH & Snavely FA 1975, Chemistry, 2nd ed, Harcourt Brace Jovanovich, New York

Arguing for a one-move adjustment

Sandbh considers the one move that will best accomodate the heritage of the literature and the wisdom of the masses

In previous posts I've argued that the literature likes to draw a distinction between the alkali/alkaline earth metals and the halogens/noble gases.

The net effective result is a three-way division of the nonmetals into halogens, noble gases, and the other nonmetals, consistent with literature references (as noted) to stronger, inactive, and weaker nonmetals.

In reflecting this division in our periodic table we need to account for the fact that we decided, quite a while ago, that the halogens were not worth a colour category. This is because we wanted to show astatine as a metalloid, which is fair enough; it's either that or a post-transition metal.

Now, when we adopted the poly-di scheme, with best intentions, the net result was that we moved three elements i.e. H, N, and O out of what the literature regards as an unnamed "other nonmetal" category, and co-located them with F, Cl, Br and I so as to form a new diatomic nonmetal category.

Looking back, that was a "seismic" move that resulted in a major misalignment with the literature.

In contrast, the current proposals (when compared to the literature) only require a one-move adjustment i.e. moving O—which is arguably the most nonmetallic of the "other nonmetals"—out of the unnamed "other nonmetals" category, and placing it with F, Cl, Br and I, consistent with the resulting five elements collectively representing the most chemically active nonmetals.

There is enough daylight between N and O to justify leaving N where it currently is, with the unnamed other nonmetals. On this point, although Double sharp has expressed the view that there is too much of a focus on elemental N and O when making categorisation decisions, the simple fact is that it is the properties of the elements themselves which contribute to the chemistry of their combined states.

While N and O have high ionisation energies and electronegativities, N has no electron affinity (which is a byproduct of its half-filled p sub-shell, a similar effect being seen in P) whereas O has quite a high electron affinity. More specifically, Massey (2000, p. 267) says, "It is possible for the Group 15 elements to achieve a rare gas electron configuration by accepting three electrons to form M^3– anions…this process is not very energetically favourable and, owing to strong inter electron repulsions, the formation of N^3– requires a huge 2130 kJ mol^–1…Electrons have more space on P, which lowers their mutual repulsion and results in the formation of P^3– requiring only about 1450kJ."

Consequently very little of the chemistry of nitrogen is that of simple ions and nearly all its compounds are covalent, whereas oxygen (with an electronegativity surpassed only by F) and the rest of the halogens readily form simple ions and ionic compounds.

Now, chemical reactions yielding N₂ are, as a rule, explosive but this is an outcome of nitrogen in compounds very much preferring to form a highly stable triatomic bond to itself  and does not represent a generalised nonmetallic property. The same triatomic bond is responsible for elemental nitrogen's inertness. Whereas the eagerness of oxygen and the halogens to combine with other elements generally is characteristic of "strong" nonmetals.

Agonising about the distinguishability of sulfur v iodine, or nitrogen v oxygen (or even iodine), is not consistent with the literature. According to the literature, the halogens are regarded as the epitome of non-metallic character and, in this sense, N, O and S are regarded as "other nonmetals". We have rightly removed astatine from this epitome category thereby increasing the category's nonmetallic calibre. The proposals before us, involving a one-move adjustment of O, would further enhance the nonmetallic character of the corrosive nonmetals category, and reduce the nonmetallic character of the "other nonmetals" category, to boot.

I don't claim that the resulting schemes are perfect. Indeed, Double sharp has noted that N is capable of forming hydrogen bonds, and coordination complexes by donating its lone pairs of electrons. That is fine if you want to drill down into the detail: I further note that H-bonds formed by S (like those formed by N) are normally also considered to be be strong, despite the lower electronegativity of S; and that C, P, and S (like N) are also capable of acting as ligands. So what? Classification schemes are often characterised by boundary overlaps, just as our current scheme is. I only claim that the proposed schemes are pragmatic minimalist constructs that are the closest we are going to get to the way the nonmetals are broadly conceived of in the literature (which is not at the drill-down level).

In summary it seems to me that whereas the current three-move scheme was "seismic", and a two-move scheme involving O and  N would be needlessly controversial, a one-move scheme would be "minimalist".

I'll still do a sandbox come what may; this "seismic v one-move" perspective only occurred to me recently, and I wanted to post it in case it chimed with any other project members.

Nitrogen article

Nitrogen may be usefully compared to its horizontal neighbours carbon and oxygen as well as its vertical neighbours in the pnictogen column (phosphorus, arsenic, antimony, and bismuth).

Like carbon, nitrogen is limited to a maximum covalency of four. In its compounds, particularly in biochemistry, it is capable of forming hybrid orbitals analogous to those seen in carbon. Examples include ammonia and amines (sp³ tetrahedral); histidine, purines, and pyrimidines (sp² planar); and nitrogen gas and cyanide (sp linear). (Beckman 2000, pp. 18–19)

Its proclivity for catenation is less than that of carbon but more than that of oxygen. The longest chain of nitrogen yet synthesised has eleven atoms (C is unlimited; O has an effective limit of three).

Nitrogen resembles oxygen in its capacity to form hydrogen bonds and coordination complexes by donating its lone pair of electrons. Its high electronegativity, while comparable to that of oxygen, has been described as "misleadingly high" (Phillips & Williams 1965, p. 609) on account of nitrogen's negative electron affinity.

One property nitrogen shares with its horizontal neighbours is preferentially forming multiple bonds, typically with carbon, nitrogen, or oxygen atoms, through p_π – p_π interactions; thus, for example, nitrogen occurs as a diatomic molecule and thus has very much lower melting (−210 °C) and boiling points (−196 °C) than the rest of its group, as the N₂ molecules are only held together by weak van der Waals interactions and there are very few electrons available to create significant instantaneous dipoles. This is not possible for its vertical neighbours; thus, the nitrogen oxides, nitrites, nitrates, nitro-, nitroso-, azo-, and diazo-compounds, azides, cyanates, thiocyanates, and imino-derivatives find no echo with phosphorus, arsenic, antimony, or bismuth. By the same token, however, the complexity of the phosphorus oxoacids finds no echo with nitrogen (Greenwood p. 412).

Nitrogen has a less-well known diagonal relationship with sulfur, manifested in like charge densities and electronegativities (the latter are identical if only the p electrons are counted; see Hinze and Jaffe 1962) especially when S is bonded to an electron-withdrawing group. They are able to form an extensive series of seemingly interchangeable sulfur nitrides, the most famous of which, polymeric sulfur nitride, is metallic, and a superconductor below 0.26 K. The aromatic nature of the S₃N₂²⁺ ion, in particular, serves as an exemplar of the similarity of electronic energies between the two nonmetals (Rayner-Canham 2011, p. 126).

Quotes from the literature

Are here.

Classifying the elements (A)

Symmetry in the periodic table
The progression from metallic to nonmetallic character in traversing the periodic table shows a pleasing symmetry

Electroactive metals Groups 1–3, Ln, An			Corrosive nonmetals O, F, Cl, Br, I
Transition metals (mundane) Most of 'em			Intermediate nonmetals H, C, N, P, S, Se
Poor metals Ga, Bi etc			Weak nonmetals (metalloids) B, Si, Ge, As, Sb, Te
Noble metals Ru, Rh, Pd, Ag, Os, Ir, Pt, Au			Noble gases He, Ne, Ar, Kr, Xe, Rn

Notes

1.	Noble metals are a subgroup of the transition metals
2.	Corrosive nonmetals are corrosive, and highly electronegative (> 2.6), and are, or their species are, capable of acting as relatively strong oxidising agents
3.	The more moderate nature of the intermediate nonmetals is relatively self-evident, situated as they are between the corrosive nonmetals and the weak nonmetals. The magic thread  that binds the intermediate nonmetals goes H → C → P → N → S → Se: Chemical similarities between H and C were discussed by Cronyn (2003). They include proximity in ionization energies, electron affinities and electronegativity values; half-filled valence shells; and correlations between the chemistry of H–H and C–H bonds. C and P represent an example of a less-well known diagonal relationship, especially in organic chemistry. Spectacular evidence of this relationship was provided in 1987 with the synthesis of a ferrocene-like molecule in which six of the C atoms were replaced by P atoms. Further illustrating the theme is the extraordinary similarity between low coordinate P compounds and unsaturated C compounds, and related research into organophosphorus chemistry. P and N are in the same group. But: "In spite of their similarities, the chemistries of nitrogen and phosphorus are very different." (Wiberg 2001, p. 686) OTOH: "Although N and P show many similarities in their compounds, nitrogen and its oxides are gases whereas phosphorus and its oxides are solids." (Malati 1999, p. 83). Then again, P and N form an extensive series of phosphorus-nitrogen compounds with chain, ring and cage structures. And the P-N repeat unit in these structures bears a strong resemblance to the S-N repeat unit found in the wide range of sulfur-nitrogen compounds (Wisian-Neilson, Alcock & Wynne 1994, p. 345) as discussed next. N and S have a (less-well known) diagonal periodic table relationship, manifested in like charge densities and electronegativities (the latter are identical if only the p electrons are counted; see Hinze and Jaffe 1962) especially when S is bonded to an electron-withdrawing group. They are able to form an extensive series of seemingly interchangeable sulfur nitrides, the most famous of which, polymeric sulfur nitride, is metallic, and a superconductor below 0.26 K. The aromatic nature of the S3N22+ ion, in particular, serves as an exemplar of the similarity of electronic energies between the two nonmetals. S and Se are in the same group; "As in the case of the halogens, the chemical similarities, at least for sulfur and selenium, are abundantly obvious." (Scerri 2007, p. 49)
4.	Some authors count metalloids as nonmetals with weakly nonmetallic properties and that is the approach I have taken here.
5.	This classification scheme, as a bonus, appears to better reflect physical changes in metallic character better than is the case with scheme (B), below.
6.	I find the combination of symmetry (as in the complimentary categories) and asymmetry (many metals/few nonmetals); and the thread that links the nonmetals in the intermediate category, to be pleasing.
7.	Arguably, there may be some discontinuities and boundary overlaps. "Though classification is an essential feature of all branches of science, there are always hard cases at the boundaries. The boundary of a class is rarely sharp…Scientists should not lose sleep over the hard cases. As long as a classification system is beneficial to economy of description, to structuring knowledge and to our understanding, and hard cases constitute a small minority, then keep it. If the system becomes less than useful, then scrap it and replace it with a system based on different shared characteristics." (Jones 2010, pp. 170–171)

Thoughts

The reactive metals and mundane transition metals have distinctive chemistries. I'm reasonably sure this is the case for the poor metals, too. Do the noble metals have a distinctive chemistry, in addition to being transition metals? I don't know.

The corrosive nonmetals have distinctive chemistries, as do the weak nonmetals and the noble gases. I suspect the intermediate nonmetals do too, certainly in the way they combine with metals to yield the different kinds of hydrides, carbides, nitrides, phosphides; and I think sulfides and selenides may behave the same way---not that sure about the last two. Would like to check oxygen, to see to what degree it forms ionic, metallic, covalent, or interstitial oxides with metals, or are metal oxides mainly ionic? Never had to consider this before.

The literature

• Noble metals. It seems they do have a signature chemistry: Noble Metals, Analytical Chemistry of . Or try this 624-page whopper  from 1966. Or Noble Metals and Biological Systems.

—————

• Intermediate nonmetals. The hydrides, carbides, nitrides, phosphides, sulfides and selenides of the metals are all either ionic/saline, metallic/interstitial, or covalent.
• Phosphorous and nitrogen. Cotton and Wilkinson say that P, like N, is essentially covalent in all of its chemistry. So much for the high electronegativity of N.

—————

• Oxygen as a corrosive nonmetal. "…oxygen is a potent, reactive, and corrosive gas…liable to generate free radicals, highly reactive bleachlike compounds that burn up organic molecules. We are able to tolerate an oxygen-rich environment only because our cells possess complex biochemical mechanisms for suppressing its many harmful influences." (Ball 2013, p. 232) ✦ "In the United States alone, more than $10 billion is lost each year to corrosion…Much of this corrosion is the rusting of iron and steel…The oxidizing agent causing all of this corrosion is usually oxygen." (Joesten, Hogg & Castellion 2007, p. 217). ✦ "Oxygen is super dangerous; it’s a corrosive gas…".
• Oxygen and fluorine. "Fluorine tends to bring out the highest valence of the element with which it combines. In this its shows a strong resemblance to oxygen. In combination with metals, oxygen appears to be the best for the highest valences, e.g. OsO₄ and KMnO₄, but fluorine appears best if the highest valence is relatively low, e.g. for CoF₃, CuF₃, AgF₂, TbF₄, and BrF₅. With non-metals the difference between oxygen and fluorine is less apparent." (Phillips & Williams, p. 446)
• Oxygen and chlorine. "Chlorination reactions have many similarities to oxidation reactions. They tend not to be limited to thermodynamic equilibrium and often go to complete chlorination. The reactions are often highly exothermic. Chlorine, like oxygen, forms flammable mixtures with organic compounds." (Kent 2010, p. 104).
• Metal oxides. Most are are ionic and contain the O^2– ion. Cotton & Wilkinson say that (a) there are great differences between the chemistry of sulfur and oxygen; and (b) some oxides with transition metals in very low oxidation states are metallic e.g. NbO. Wiberg, however, says NbO is ionic—go figure.
• Metal oxide types. Phillips and Williams (1965, p. 478) have a nice table classifying the oxides. So, yes metal oxides are often ionic. The only ones shown as covalent are MO₃ for groups 6 and 7; M₂O₇ for group 7; and MO₄ for group 8. The following oxides are shown as being often metallic: MO in groups 4–6 and 8; M₂O₂ in group 1; M₂O₃ in group 4; and MO₂ in groups 1 and 2.

—————

• Metal halides 1. Greenwood & Earnshaw (2nd ed., p. 823) say that, "The majority of pre-transition metals (Groups 1, 2) together with group 3, the lanthanides and the actinides in the +2 and +3 oxidation states [the reactive metals!] form halides that are predominately ionic in character, whereas the non-metals and metals in high oxidation states (≥ +3) tend to form covalent molecular halides." They go on to note the tendency of the refractory transition metals to form cluster halides.
• Metal halides 2. "Most metal halides are substances of predominately ionic character, although partial covalence is important in some." (Cotton & Wilkison, p. 554)
• Iodides. Eagleson says the group 1 and 2 iodides are ionic and water-soluble while a few heavy-metal iodides are insoluble—AgI, CuI, HgI₂ and TlI.
• Halide types. Phillips and Williams (p. 432) say that the electronegativity values of the halogens are among the highest in the periodic table so that many of their compounds are expected to contain negatively charged halogen ions. Despite the substantial differences between the individual halogens, their compounds are sufficiently similar to permit a collective classification (p. 433). ✦ "The elements in the middle of the perioidic table form hydrides which are mostly metal-like or interstitial, although rather unstable 'covalent' hydrides can also be formed by some of the metals. There are no directly equivalent compounds among the halides. The nearest parallels occur in the low-valence iodides such as TiI2 and NbI4, which are grossly defect, and semiconductors or metals…In general, however, the halogen atoms are themselves too electronegative to enter into an alloy-like structure, and they are too large—particularly when carrying some negative charge—to be accommodated in the interstices of the metal structure. Instead, there is a large class of semi-ionic halides, often consisting of layer, or less commonly chain lattices. Such structures will require some appreciable binding between the halogen atoms, and are noticeably absent among the fluorides in contrast to the chlorides, bromides, and iodides. Within the layers the pattern retains something of the ionic type lattice, but the layers are held together by van der Waal's forces between adjacent halogen atoms. A characteristic feature of such lattices is the unsymmetric environment of the halogen atom as compared to its environment in the ionic crystal. In one direction it resembles an ionic while in another a simple molecular crystal. Such structures are therefore intermediate between those which occur with halides of the elements at the two ends of the Periodic Table." (pp. 434–435). ✦ The periodate/iodate couple is the most oxidising among the halogen oxyacids (p. 459).
• Halide structures. Wells (pp. 408–409) says many fluorides and oxides of similar formula-type are isostructural, while chlorides, bromides and iodides often have the same types of structure as sulfides, selenides and tellurides. The great majority of halides MX, MX₂, and MX₃ adopt 3D complex structures, and most monohalides and most fluorides MF₂ and MF₃ crystallise with highly symmetrical structures suited to essentially ionic crystals. Golden-yellow ThI₂ exhibits metallic conduction (p. 415).
• Halogens. "With the exception of the Li–Cs group there are closer similarities within the group than in any other in the Periodic Table." (Cotton & Wilkison, p. 547)

—————

• Periodic table of diatomic molecules" In 1979 Ray Hefferlin published a periodic ordering of all of the diatomic molecules that could result from combinations of the first 118 elements of the periodic table". I have to get me one of these.

Alkali metal

Alkaline earth metal

Lan­thanide

Actinide

Transition metal

Post-​transition metal

Weak nonmetal (metalloid)

Intermediate nonmetal

Corrosive nonmetal

Noble gas

Classifying the elements (B)

		Noble gases He, Ne, Ar, Kr, Xe, Rn
Reactive metals Groups 1–3, Ln, An			Corrosive nonmetals O, F, Cl, Br, I
Transition metals Most of 'em			Liminal nonmetals N, S, Se
Poor metals Ga, Bi etc			Weak nonmetals H, C, P
		Metalloids B, Si, Ge, As, Sb, Te

Electrochemical strength

Metals

Table 1: Metals and nonmetals

Reactive metals Strong to moderate (mostly strong)	Corrosive nonmetals Strong
Transition metals Strong to noble (mostly intermediate)	Liminal nonmetals Moderate to weak
Poor metals Moderate to weak (mostly weak)	Weak nonmetals Weak

The reactive metals (see tables 1 and 2) undoubtedly start at "strong", and are undoubtedly mostly strong. (Aluminium is included here).

Table 2: Average E⁰for metals,
stable species, pH 0, –3.0 to 3.0 V

Cohort	Highest	M	Lowest	M
Reactive	–3.04	Li	–0.20	Am
Transition	–1.7	Hf	1.52	Au
Poor	–0.76	Zn	0.98	At

The start of the transition metals is a bit blurry. If they are taken to include group 3 then they certainly start at strong. If not then even some of the group 4 metals have relatively high average reduction potentials: Hf –1.7 and Zr –1.55; and Ti is "only" –0.87. The eight noble metals are undoubtedly weak. So, strong to weak sounds OK. If group 3 and 12 are excluded, that leaves 24 metals. Eight of these are noble ("very weak"). Which ones are strong is a bit blurry, but say Hf –1.7 and Zr –1.55 (the next most "reactive" is Nb at –0.93, so that looks like a natural break). That leaves 14 moderate to weak metals. So the range is strong to noble, with most being moderate to weak. If Sc (–2.03) and Y (–2.37) in group 3 are included as transition metals, that changes the count to 4 strong, 14 moderate to weak, and 8 noble. If group 12 are also included as transition metals, that changes it to 4 strong, 17 moderate to weak, and 8 noble.

Among the poor metals, Zn (–0.76) and Ga (–0.53) have reduction potentials that are reasonably electropositive, but these metals are regarded by Rayner-Canham and Overton (2006, pp. 29–30) as chemically weak. Cadmium (–0.44) and indium (–0.34) are next but they are not, as far I know, generally regarded as chemically weak metals, although Steele (1966, pp. 67–68) says that "in their reactions the metals show weak electropositive character." The rest of the poor metals have positive reduction potentials, so they can be described as weak. The approximate count is two moderate and nine weak. If the group 12 metals are counted as transition metals the count would be one moderate and seven weak. So the poor metals are mostly weak.

If aluminium is counted as a poor metal how can it be accommodated as such given its respectable –1.65 electrode potential? Stott (1956, p. 100) says that a lot of the chemistry of aluminium suggests it is a comparatively weak metal and that in many ways it is weaker than transition metals such as iron, nickel, cobalt and manganese, all of which have lower electrode potentials. Steele (1966, p. 60) notes the paradoxical chemical behaviour of aluminium: "It resembles a weak metal in its amphoteric oxide and in the covalent character of many of its compounds ... Yet it is a highly electropositive metal ... [with] a high negative electrode potential". Kneen, Rogers and Simpson (1972, p. 363) say that aluminium "is only moderately electropositive…". Moody (1991, p. 300) says that, "aluminium is on the "diagonal borderland" between metals and non-metals in the chemical sense." Rayner-Canham and Overton (2006, pp. 29–30) count it as a chemically weak metal.

Categorising the metals is based on more than just their electrode potentials. So I think the categorisation of aluminium is neither here nor there (it's either moderate or weak).

Nonmetals

Table 3: Average E⁰ for nonmetals,
stable species, pH 0, –3.0 to 3.0 V

Strong	Fluorine: F2 + 2e → 2HF = 2.87 Oxygen: O3 + 2e → O2 = 2.08; O2 + 4e → 2H2O = 1.23; then (2.08 + 1.23)/2 = 1.65 Bromine: BrO4– + 2e → BrO3– = 1.85; 2BrO3– + 10e → Br2 = 1.48; Br2 → 2Br– + 2e = 1.07; then (1.85 + 1.48 + 1.07)/3 = 1.46 Chlorine: 2ClO4– + 14e → Cl2 = 1.38; Cl2 + 2e → 2Cl– = 1.36; then (1.38 + 1.36)/2 = 1.37 Iodine: H5IO6 + 2e → IO3– = 1.6; 2IO3– + 10e → I2 = 1.19; I2 +2e → 2I– = 0.53; then (1.6 + 1.19 + 0.53)/3 = 1.1
Moderate	Sulfur: S2O8–2 → 2HSO4– = 2.06; HSO4– + 6e → S = 0.39; S + 2e → H2S = 0.14; then (2.06 + 0.39 + 0.14)/3 = 0.86 Nitrogen: 2NO3– → N2 = 1.25; N2 + 6e → 2NH4– = 0.27; then (1.25 + 0.27)/2 = 0.76 Selenium: HSeO4– → H2SeO3 = 1.15; H2SeO3 + 4e → Se = 0.74; Se + 2e → H2Se = –0.11; then (1.15 + 0.74 – 0.11)/3 = 0.59
Weak	Carbon: CO2 + 4e → C = 0.21; C + 4e → CH4 = 0.13; then (0.21 + 0.13)/2 = 0.17 Phosphorus: H3PO4 → PH3 = –0.28 Hydrogen: 2H+ + 2e → H2 = 0.0; H2 + 2e → 2H– = –2.25; then (0.0 – 2.25)/2 = –1.12

Average standard reduction potentials provide a reasonable demarcation (see table 3). Although nitrogen has a high electronegativity it is a poor oxidising agent. Only when it is in a positive oxidation state (i.e. in combination with oxygen or fluorine) are its compounds good oxidising agents but even then their reactivity is often limited by kinetic factors (Cox 2004, p. 161).

Table 4 lists a similar nonmetal demarcation based on bonding strengths with F, O and Cl (Synder 1966, p. 242).

Table 4: Nonmetal groupings (Synder 1966)

Bond strength
High	O, F, Cl, Br, I
Moderate	C, N, S, Se
Weak	H, P

Table 5 is an electrochemical series given by Nelson (2011, pp. 55, 57). He wisely writes, "In using the series, care needs to be taken to remember that it is only an approximation, and can only be used as a rough guide to the properties of the elements. Provided that this is done, however, it constitutes a very useful classification, and although purists often despise it because of its approximate nature, the fact is that practising chemists make a great deal of use of it, if only subconsciously, in thinking of the chemistry of different elements."

Table 5: Nonmetal groupings (Nelson 2011)

Strongly electronegative	O, F
Moderately electronegative	Br, Cl
Weakly electronegative	C, N, S, I
Approximately electro-neutral	H, P

Reactivity

Nonmetal	Electron affinity kJ/mol	Electro- negativity	Enthalpy of dis- sociation kJ/mol	Average electrode potential V	Caustic?	Corrosive?	Pyro- phoric?	HSAB	Direct noble gas com- pounds?	Reactivity boxes
F	334	3.98	159	2.87	1	1	0	H	Y	8
Cl	355	3.16	242	1.37	1	1	0	H/B	P	7.25
Br	331	2.96	193	1.46	1	1	0	B/S	N	6.25
O	147	3.44	498	1.65	0	1	0	H	N	4
I	301	2.66	151	1.1	1	1	0	S	N	5
S	207	2.58	266	0.86	0	0	0	S	N	3
Se	201	2.55	332	0.59	0	0	0	S	N	2
P	78	2.19	198	-0.28	0	0	0	S	N	1
N	0	3.04	945	0.76	0	0	0	B	N	1.5
H	79	2.20	436	-1.12	0	0	0	H	N	1
C	128	2.55	346	0.17	0	0	0	S	N	0
Average	196	2.85	342	0.85

Notes: (a) Caustic = destructive of organic tissue; (b) If a particular property is quantitative, the last row gives the average value of the listed nonmetals.

Yellow shading denotes nonmetals with an above average value for that property.

Aqua shading denotes an intermediate value. If a property is binary (e.g. Caustic?) then the distinction between above average and below average is self-explanatory. For the HSAB rating I've assigned a value of 1 to 'hard' (H); a value of 0.5 to borderline (B); and a value of 0 to 'soft' (S). If a nonmetal is sometimes listed as more than one HSAB category, I've assigned it the average of the applicable values. In the Forms noble gas compounds? column, Cl has a value of P (for possibly) since that's the way I interpreted the literature on this question.

Light grey shading denotes a below average value. This works the other way around in the case of enthalpy of dissociation.

Gold shading, as seen only in the last column, denotes an intermediate (electromoderate) nonmetal.

The last column shows how many "above average" property boxes a particular nonmetal has checked. Since nine is the greatest number of property boxes that can be checked it follows that > 4.5 boxes is above average and < 4.5 is below average. The Pyrophoric? column is a holdover from when white P was counted here. If we are comparing apples with apples i.e. the most thermodynamically stable forms of the elements with one another, it probably needs to go.

Enthalpy of dissociation (or element bond strength) is associated with reactivity: "The high dissociation enthalpy of the O₂ molecule, 498 kJ/mol, is the reason that molecular O. is relatively unreactive and its reactions usually require thermal or photochemical activation." (Eagleson 1994, p. 768) The figure for P is for white P, as far as I know; the figure for black P is likely to be quite a bit higher which means its figure of merit will go down to 0. OTOH, this site says that figure for black P is only 43 kJ/mol higher, which means it wouldn't.

On the basis of the above table, nonmetals of above average or high reactivity are F, Cl, Br, O, and I, an outcome that is consistent with the literature.

References

• Ball P 2001, Life's matrix: A biography of water, University of California Press, Berkeley
• Cotton FA, Wilkinson G, Murillo CA & Bochmaan M 1999, Advance inorganic chemistry, 6th ed., John Wiley & Sons, New York
• Cox PA 2004, Inorganic chemistry, 2nd ed., BIOS Scientific Publishers, London: "Nitrogen is a moderately electronegative element…"
• Cronyn MW 2003, "The proper place for hydrogen in the periodic table", Journal of Chemical Education, vol. 80, no. 8, pp. 947–950, doi:10.1021/ed080p947
• Eagleson M 1994, Concise encyclopedia chemistry, Walter de Gruyter, Berlin
• Greenwood NN & Earnshaw A 1998, Chemistry of the elements, 2nd ed., Butterworth-Heinemann, Oxford
• Hinze J & Jaffe HH 1962, "Electronegativity. I. Orbital electronegativity of neutral atoms", Journal of the American Chemical Society, vol. 84, no. 4, pp. 540–546, doi:10.1021/ja00863a008
• Joesten MD, Hogg L, Castellion ME 2007, The world of chemistry: Chemistry essentials, 4th ed., Thomson Brooks/Cole, Belmont, California
• Jones BW 2010, Pluto: Sentinel of the outer Solar System, Cambridge University Press, Cambridge
• Kent JA 2007, Kent and Riegel's Handbook of industrial chemistry and biotechnology, 11th ed., vol. 1, Spring Science + Business Media, New York
• Malati MA 1999, Experimental inorganic/physical Chemistry: An investigative, integrated approach to practical project work, Woodhead Publishing, Oxford
• Moody B 1991, Comparative inorganic chemistry, 3rd ed., Edward Arnold, London
• Nelson PG 2011, Introduction to inorganic chemistry: Key ideas and their experimental basis, Ventus Publishing ApS
• Phillips CSG & Williams RJP 1965, Inorganic chemistry, vol. 1, Principles and non-metals, Clarendon Press, Oxford
• Rayner-Canham G & Overton T 2006, Descriptive inorganic chemistry, 4th ed., WH Freeman and Company, New York
• Kneen WR, Rogers MJW & Simpson P 1972, Chemistry: Facts, patterns and principles, Addison-Wesley Publishers, London
• Scerri E 2007, The Periodic Table: Its story and its significance, Oxford University Press, Oxford
• Schweitzer GK & Pesterfield LL 2010, The aqueous chemistry of the elements, Oxford University Press, Oxford, pp. 228–229; 232–233
• Steele D 1966, The chemistry of the metallic elements, Pergamon Press, Oxford
• Stott RW 1956, A companion to physical and inorganic chemistry, Longmans, Green and Co., London
• Synder MK 1966, Chemistry: Structure and reactions, Holt, Rinehart and Winston, New York
• Wells AF 1984, Structural inorganic chemistry, 5th ed., Clarendon Press, Oxford
• Wiberg N 2001, Inorganic chemistry, Academic Press, Berlin
• Wisian-Neilson P, Alcock HR, Wynne KJ (eds) 1994, Inorganic and organometallic polymers II: advanced materials and intermediates, American Chemical Society, Washington DC
• Wulfsberg G 2000, Inorganic chemistry, University Science Books, Sausalito, California, pp. 247–249; 273–276

Blocks to blocs

Order	Type
0th	Main group elements (typically colourless salts)		Transition elements (typically coloured salts)
1st	s block	p block	d block	f block
2nd	s(d) bloc	p(s) bloc	d(s) bloc	f(dp) bloc
3rd	H, Be	Al	Group 11	-- solid state configurations of Ln and An -- f-orbital involvement seen in early An

Metals

Basic metals

aka post-transition metals

Incipient metals

https://www.chemistryworld.com/news/bonding-rethink-called-for-as-new-metavalent-bond-proposed/3009908.article

Magnetic liquid metals

• www.cnet.com/news/scientists-create-liquid-metal-that-stretches-like-terminator/
• https://www.eurekalert.org/pub_releases/2019-03/acs-lm032019.php
• https://pubs.acs.org/doi/abs/10.1021/acsami.8b22699

Molecular metals

Polythiazyl; gallium

Differentiating electron scale

An optimal block is a periodic table block in which the proportion of elements that have a predominance of either s-, p-, d-, and f- differentiating electrons, as applicable, is maximised.

The idea of an optimal block has its roots in the work of Scerri and Parsons (2018, p. 151):

“…for the purposes of selecting an optimal periodic table we prefer to consider block membership as a global property in which we focus on the predominate differentiating electron. We readily acknowledge the fact that the atoms of Mn, Zn, Tc, Cd, Pt [?], Hg, Lr, La, Gd, Ac, Th, and Cm are all anomalous in that they have a differentiating electron that is atypical of the block that they are situated in. These anomalies should not challenge our attempts to establish the overall structure of the periodic table in terms of sequences of blocks in the periodic table and as a result our recommendations for the membership of group 3 of the periodic table.”

DIFFERENTIATING ELECTRON SCALE OF PERIODIC TABLES

Table                        #  Notes
===========================================================================
0.   Madelung rule (1928)    0  Idealised form
---------------------------------------------------------------------------
11.  La-Ac w/HeBe           11  Physics-based optimal block solution
---------------------------------------------------------------------------
12a. LSPT                   12  Elegant 32-column version showing theoretical tetrahedral symmetry
---------------------------------------------------------------------------
12b. Lu-Lr w/HeBe           12  18-column version of LSPT
---------------------------------------------------------------------------
12c. La-Ac w/HeNe           12  Recommended for IUPAC as it places He over Ne
---------------------------------------------------------------------------
13a. Lu-Lr w/HeNe           13  A compromise (?) between 12c. and 14a
---------------------------------------------------------------------------
13b. Volumetric (1949)      13  La-Ac, He-Ne, and groups 11–12 as s-block members, here
---------------------------------------------------------------------------
14a. IUPAC, current         14  Further along the chemistry end of the scale, here
---------------------------------------------------------------------------
14b. Metallurgist's (1994)  14  La-Ac w/HeNe, HF, and AlSc, here
---------------------------------------------------------------------------
15.  Remy’s (1956)          15  La-Ac w/H-F, Th-Pa-U as d-block elements, and Np+ as transuranic elements, analogous to Pm+, here
---------------------------------------------------------------------------
17.  Rayner-Canham (2002)   17  aka the Inorganic Chemist's Periodic Table, here
---------------------------------------------------------------------------
21.  Pauling (1980)         21  La-Ac w/HeNe; Sc-La as s-block;* Th–Pu as d-block and as f-block; Ku (104) as f-block
    
 # = differentiating electron discrepancies
 * Pauling's table is ambiguous but in the text he treats Sc, Y, and La as the congeners of B and Al

References

• Atkins P 2004, Galileo's finger: The ten great ideas of science, e-book ed., Oxford University, Oxford
• Pauling L 1980, General chemistry, 3rd ed., Dover Publications, New York, p. 135
• Rossotti H 1998, Diverse atoms: Profiles of the chemical elements, Oxford University, Oxford
• Scerri E 2004, "The best representation of the periodic system: The role of the n + l rule and of the concept of an element as a basic substance", in DH Rouvray and RB King, The periodic table: Into the 21st century, Research Studies Press, Baldock, England
• Scerri ER & Parsons W 2018, "What elements belong in group 3 of the periodic table?", in ER Scerri & G Restrepo (eds), Mendeleev to Oganesson: A multidisciplinary perspective on the periodic table, Oxford University Press, New York, [17], pre-publication draft here
• Schwarz WHE & Rich RL 2010, "Theoretical basis and correct explanation of the periodic system: Review and update", Journal of Chemical Education, vol. 87, no. 4, pp 435–443
• Stewart PJ 2018, "Tetrahedral and spherical representations of the periodic system", Foundations of Chemistry, vol. 20, no. 2, pp. 111–120

LST

I’ve been looking at the LST for quite a while and...I don’t get why some folks prefer it:

Left-step periodic table (by Charles Janet)

f1

f2

f3

f4

f5

f6

f7

f8

f9

f10

f11

f12

f13

f14

d1

d2

d3

d4

d5

d6

d7

d8

d9

d10

p1

p2

p3

p4

p5

p6

s1

s2

1s

H

He

2s

Li

Be

2p 3s

B

C

N

O

F

Ne

Na

Mg

3p 4s

Al

Si

P

S

Cl

Ar

K

Ca

3d 4p 5s

Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn

Ga

Ge

As

Se

Br

Kr

Rb

Sr

4d 5p 6s

Y

Zr

Nb

Mo

Tc

Ru

Rh

Pd

Ag

Cd

In

Sn

Sb

Te

I

Xe

Cs

Ba

4f 5d 6p 7s

La

Ce

Pr

Nd

Pm

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

Hf

Ta

W

Re

Os

Ir

Pt

Au

Hg

Tl

Pb

Bi

Po

At

Rn

Fr

Ra

5f 6d 7p 8s

Ac

Th

Pa

U

Np

Pu

Am

Cm

Bk

Cf

Es

Fm

Md

No

Lr

Rf

Db

Sg

Bh

Hs

Mt

Ds

Rg

Cn

Nh

Fl

Mc

Lv

Ts

Og

Uue

Ubn

f-block

d-block

p-block

s-block

This form of periodic table is congruent with the order in which electron shells are ideally filled according to the Madelung rule, as shown in the accompanying sequence in the left margin (read from top to bottom, left to right). The experimentally determined ground-state electron configurations of the elements differ from the configurations predicted by the Madelung rule in twenty instances, but the Madelung-predicted configurations are always at least close to the ground state. The last two elements shown, elements 119 and 120, have not yet been synthesized.

MRD: The states crossed by same red arrow have same $n+\ell$ value. The direction of the red arrow indicates the order of state filling.

It has the following features: (a) it is more regular than the conventional table; (b) it has no gaps; (c) each element in every second row of each block starts a triad; (d) each element in each period has an n+l value matching the period number i.e. it matches the diagonal lines of the Madelung rule diagram (MRD); and (e) the first row anomaly becomes clearer i.e. s >> p > d > f.

(a) means the period lengths go 2, 2, 8, 8, 18, 18, 32, 32 whereas the conventional form goes 2, 8, 8, 18, 18, 32, 32;
(b) means e.g. there is no gap between Be and B;
(c) means e.g. that Tc, Re, and Bh form a triad;
(d) means e.g. that the n+l value of Ti, in period 5, is 3 + 2 = 5. Here, n is the principal quantum number (same as the orbital value of 3, in 3d); and l is the azimuthal quantum number, where s = 0; p = 1; d = 2; f =3). Sr, in the same period, is 5s = 5 + 0 = 5; and
(e) is nice.

Feature (d) doesn’t mean much since, like the MRD, the quantum numbers involved are based on idealised rather than actual differentiating electrons. For example, Zn is 3d = 3 + 2 = 5. Whereas in real life the differentiating electron in Zn = 4s = 4 + 0 = 4. In fact the MR is wrong in 20 places—it’s an approximation or idealisation, not a law carved in stone.

While the strongest objection to the LST is He over Be, that’s not so much of an issue. The electronegativity and ionisation energy of He can be extrapolated from the rest of the alkaline earth metals. The 1s² electron configuration matches that of the rest of group 2. We know that He is capable of acting as a metal. One just needs to colour code it as a noble gas, on account of its closed shell.

The ADOMAH periodic table is based on idealised electron quantum numbers

Proponents of the LST say its regularity and elegance, as well as its symmetry (the four blocks fit naturally into a tetrahedron or, the LST can be rearranged into the ADOMAH form) mean that it is an optimal form of periodic table.

I say that:

• these features are derived from an idealisation rather than actual physical parameters i.e. idealised v actual quantum numbers;
• as such they mean nothing in terms of an optimal periodic table;
• while the electron configuration filling sequence has some irregularities one can still see a general regularity that accords with the MR diagram;
• the general regularity hints at a hidden symmetry in the applicable laws of nature; and
• this hidden (or broken) symmetry manifests as the asymmetric conventional form.

Here’s a relevant quote:

While the laws of Nature, “are simple, symmetrical, and elegant, the real world isn’t. It’s messy and complicated…The reason is clear. We do not observe the laws of Nature: we observe their outcomes. Since these laws find their most efficient representation as mathematical equations, we might say that we see only the solutions of those equations not the equations themselves. This is the secret which reconciles the complexity observed in Nature with the advertised simplicity of her laws. Outcomes are much more complicated than laws; solutions much more subtle than equations. For, although a law of Nature might possess a certain symmetry, this does not mean that all the outcomes of the law need manifest that same symmetry.” (Barrow 2008)

It is as if the periodic table lies at the bottom of a wine bottle; the symmetry of the bottle’s base is clear from the top of the dimple in the centre, but it is hidden from any point in the valley surrounding the central dimple.* Assigning >special< significance to the LST (or the ADOMAH variation) on the basis of its elegance, regularity, symmetry, or coherence with the MRD, while well intentioned, is misguided and needlessly detracts from the clarity of the chemical relationships among the elements and their compounds.

∗ I borrowed this analogy from the EB article on Subatomic particles, Hidden symmetry section, by Sutton C, 2017

Periodic table trends (arrows show an increase)

Possibly the next biggest objection to the LST is that it makes a train wreck of the left to right metal to nonmetal progression, and associated trends.

As Ball (2010) said:

“I think it is a poor deal to trade subjective aesthetics (which clearly not everyone shares) for the long-standing traditional navigational axes that chemists use around the PT.”

Weighing up the features and drawbacks of the LST, I don’t understand how they can be reconciled.

The conventional form of the periodic table is about as good as any other; hence it is retained for want of a better alternative.

Can anyone shed light on the merits of the left-step table, such that it becomes preferred to the conventional form?

References

• Ball P 2010, comments to “The disappearing spoon” review, homunculus blog, viewed 19 May 2019, https://www.blogger.com/comment.g?blogID=26741618&postID=2980643491692822828&bpli=1&pli=1
• Barrow JD 2008, New theories of everything, Oxford University Press, Oxford, pp. 136–140

Sandbh (talk) 17:58, 14 June 2019 (UTC)

See also

• https://aeon.co/essays/beauty-is-truth-there-s-a-false-equation

Nonmetals 2019

Could we look at this again:

1. Their results likely draw on one of the biggest surveys of the literature ever attempted, for this kind of research.

2. The article says their database of [only] 3.3 million abstracts (spanning 1922 to 2018), drawing from 1,000 journals, was focussed on materials science, physics, and chemistry.

3. Key words were extracted using ChemDataExtractor ("Give it a journal article, and it will extract chemical names, properties, and spectra from the text so they can be imported into a database or spreadsheet.").

4. I agree there are a few anomalies like Fr for the very plausible reason you give. Is this not a case of "perfect is the enemy of good"?

5. Their results match with the J.Chem.Ed. Kohonen map cited in our own archive 15.

We've never had a comprehensive literature-based view of nonmetal categories, which is why we've always struggled doing a fair job with these. Now we have, what is arguably, the biggest perspective ever on the nonmetals, let alone the remarkable correlation with the rest of the periodic table.

If we confine our perspective on the periodic table to purely chemistry-based considerations (which we never have, as far as I know) we'll being doing ourselves a disservice to our readers, not to mention the periodic table.

A recent editorial in Nature Materials opined that

"There has been a synergy between our evolving understanding of the periodic table and our understanding of materials. Element position within the periodic table and sustainability considerations plays a role in determining research activity and practical applications. The space in the periodic table for new materials combinations is vast. All elements will continue to be worthy of investigation."

The key words here are a "synergy" or a working together, as guided by the periodic table, and our "evolving" understanding of the latter.

So, yes, I'm calling for a rethink of our nonmetal categories.

Metalloids in alloys (notes)

Copper-germanium alloy pellets, likely ~84% Cu; 16% Ge. When combined with silver the result is a tarnish resistant sterling silver. Also shown are two silver pellets.

Context

Writing early in the history of intermetallic compounds, the British metallurgist Cecil Desch observed that "certain non-metallic elements are capable of forming compounds of distinctly metallic character with metals, and these elements may therefore enter into the composition of alloys". He associated silicon, arsenic, and tellurium, in particular, with the alloy-forming elements.

"The metals form definite chemical compounds not only with the dissimilar non-metallic elements but also with the metalloids, and in many cases with each other. The compounds of the metals with each other, called "intermetallic compounds," do not, however show the marked evidences of chemical combination which are found in the compounds of the metals with the electronegative elements like oxygen and the halogens".

Jeffries Z & Archer RS 1923, The science of metals, McGraw-Hill, New York, p. 225

Phillips and Williams suggested that compounds of (phosphorus), silicon, germanium, arsenic, and antimony with B metals, "are probably best classed as alloys".

Boron

"The most important alloys of boron (ferroboron, calcium boron) are used in the processing of steel, cast iron, iron alloys, copper and copper alloys as deoxidants."

Erdey ‎R et al. 1965, Gravimetric analysis: International series of monographs in…, p. 204

"A superhard substance that is more slippery than Teflon could protect mechanical parts from wear and tear, and boost energy efficiency by reducing friction. The “ceramic alloy” is created by combining a metal alloy of boron, aluminium and magnesium (AlMgB₁₄) with titanium boride (TiB₂). It is the hardest material after diamond and cubic boron nitride. BAM, as the material is called, was discovered at the US Department of Energy Ames Laboratory in Iowa in 1999, during attempts to develop a substance to generate electricity when heated.

Read more.

"Interestingly, transition metal borides are metallic compounds, and they are often more conductive than the parent metal."

Carenco S et al. 2013, "Nanoscaled metal borides and phosphides: Recent developments and perspectives", Chemical Reviews, vol. 113, no. 10, pp. 7981–8065 (7992)

With lithium, boron is known to form a metallic, malleable, extrudable, and machinable compound alloy having the composition Li5B4, and a silvery metallic lustre.

Wang FE 2005, Bonding theory for metals and alloys, Elsevier, Amsterdam, p. 192

Silicon

"This book details aluminum alloys with special focus on the aluminum silicon (Al‐Si) systems – that are the most abundant alloys second only to steel."

Phosphorus

"Most of the metal phosphides are semiconductors or insulators, because their electrons are localized in the vicinity of phosphorus atoms; however, some of them (usually the most metal-rich ones) exhibit a metallic character."

Carenco S et al. 2013, "Nanoscaled metal borides and phosphides: Recent developments and perspectives", Chemical Reviews, vol. 113, no. 10, pp. 7981–8065

Germanium

"Germanium forms alloys with many metals. Harner (1961) described a partial list of 21 such metals, including all the base metals and most precious metals. About one-half of these germanium-metal systems contain intermetallic compounds. Alloys, however, are minor uses for germanium."

Butterman WC & Jorgenson JD 2005, Mineral commodity profiles germanium, US Geological Survey, Reston, Virginia

"Although relatively little germanium is used in alloy form, there are a few alloys that have proven useful. An 88-percent-gold–12-percent-germanium alloy, with a melting temperature of 359° C, has been used as a solder for gold jewellery (Brady and Clauser, 1997). Germanium also is alloyed in several combinations with gold, silver, copper, and palladium in dental alloys and with silicon in thermoelectric devices. More often, germanium is used in very small quantities as a hardener of metals, such as aluminum, magnesium, and tin."

Harner HR 1961, "Germanium", in Hampel CA (ed.), Rare metals handbook, 2^nd ed. Reinhold Publishing Co., New York, pp. 188–197.

"Germanium appears to form no carbide, but alloys with many metals and metalloids."

Rochow EG 1973, "Germanium", in Comprehensive inorganic chemistry, vol. 2, Pergamon Press, Oxford, p. 10

Arsenic

"The primary use of arsenic is in alloys of lead (for example, in car batteries and ammunition)."

"Arsenic is used as the group 5 element in the III-V semiconductors gallium arsenide, indium arsenide, and aluminium arsenide.[29] The valence electron count of GaAs is the same as a pair of Si atoms, but the band structure is completely different which results in distinct bulk properties.[30] Other arsenic alloys include the II-V semiconductor cadmium arsenide.[31]"

--- our entry for Arsenic

Antimony

"As late as the 19th century, the number of uses for antimony and the amount used remained small. Most of it was used in type metal or alloyed with lead for use as bearing metal (babbitt metal) or with tin for use in Britannia metal as candlesticks, dinnerware, eating utensils, and so forth.

Antimony is also a component of several tin-based alloys, such as britannia metal, pewter, white bearing metal (true babbitt), and a new alloy, a tin-antimony-silver solder used for joining pipes for carrying potable water.

Antimony itself is hard and brittle and is used alone only for very minor uses, such as ornamental castings. But its compatibility with lead and other low-melting-point metals make it useful in alloys."

Li T, Archer GF, and Carapella SC Jr., 1992, "Antimony and antimony alloys", in Kirk-Othmer Encyclopedia of chemical technology (4th ed.): New York, John Wiley & Sons, v. 3, p. 367-381.

Tellurium

https://www.chemistryworld.com/news/bonding-rethink-called-for-as-new-metavalent-bond-proposed/3009908.article

van Arkel-Ketelaar

Metasynthesis

Wikipedia

References

Constitution of binary alloys, by Hansen, McGraw-Hill Book Company (1958-1969)
Crystal chemistry and semiconduction in transition metal binary compounds, by Suchet 1971, Academic Press

Parsing the nonmetals (II)

"The range of chemicals studied in organic chemistry includes hydrocarbons (compounds containing only carbon and hydrogen) as well as compounds based on carbon, but also containing other elements, especially oxygen, nitrogen, sulfur, phosphorus (included in many biochemicals) and the halogens."

"The acronym CHNOPS, which stands for carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur, represents the six most important chemical elements whose covalent combinations make up most biological molecules on Earth."

"It is a long standing tradition that organic compounds of the metalloids fall within scope of the definition of organometallic compounds."

Corrosive nonmetals

Compounds of the corrosive nonmetals number among the range of chemicals studied in organic chemistry.

Intermediate nonmetals

Covalent combinations of the first five of these (along with the corrosive nonmetal oxygen) make up most biological molecules on Earth.

Metalloids

It is a long standing tradition that organic compounds of the metalloids fall within scope of the definition of organometallic compounds.

Compounds formed with metals

Category	Elements	Compound types	Other types	Notes
Corrosive nonmetal	F, Cl, Br, I, O	Ionic	Interstitial (O)	For M = metal and N = nonmetal, interstitial and intermetallic compounds feature M-M (metallic), M-N (ionocovalent), and N-N (covalent) bonding contributions. In N-poor compounds metallic bonding predominates; in N-rich compounds covalent bonding predominates.
Intermediate nonmetal	H, C, N, P, S, Se	Salt-like to covalent	Interstitial (H, C, N); intermetallic (P?, Se)
Metalloid	B, Si, Ge, As, Sb, Te	Salt-like to more covalent; alloys	Interstitial (B); intermetallic
Metal	Many	Alloys	Intermetallic	The d-electrons in the partially-filled orbitals of transition metal atoms form covalent bonds with their counterparts in other transition metal atoms

The importance of symmetry

Brooks M 2018, New Scientist, 18 Aug 2018, no. 3191, p. 30:

Knowing where new particles may be hiding is a tricky business. The most powerful searchlight at our disposal is symmetry: the idea that something looks and behaves the same even when some aspect of its position, direction or orientation is changed. A circle, for example, has total rotational symmetry, while a square has broken rotational symmetry – it looks the same when you turn it through multiples of 90 degrees, but not under any other rotation.

When a symmetry is broken, physicists sit up and take notice. “Symmetry-breaking doesn’t just happen – there’s always some reason behind it,” says physicist David Tong at the University of Cambridge.

This is especially true of the more complicated symmetries that arise in particle physics. Rather than rotate a particle or move it about, you might swap it for its oppositely charged antiparticle. If you see no difference in their interactions, that is a symmetry. For example, two electrons repel each other in exactly the same way as two positrons do, displaying identical physics under the reversal of charge. We call that charge symmetry.

Flipping important
Another key symmetry is time reversal. Imagine you are watching a recording of a snooker match on TV, and you see a ball glance off the cushion. You press rewind, and you now see the ball move back towards the cushion. If it comes off at a different angle to what you saw before, time-reversal symmetry is broken.

The third fundamental symmetry is parity symmetry. This time, while watching the snooker match you see the initial shot reflected in a mirror. If it comes off the cushion at a different angle in the mirror view, this breaks parity symmetry.

Sometimes you don’t have to actually spot a symmetry being broken – just where it should be broken but isn’t. In 1964, for instance, Murray Gell-Mann applied symmetry considerations to the standard model of particle physics and came up with the idea that there should exist a set of particles that, put together in certain ways, would make the protons and neutrons we find in the atomic nucleus. Gell-Mann’s mathematical hunch was right on the money: his conjectured “quarks” were found in subsequent particle searches, and Gell-Mann won a Nobel prize in physics for his efforts.

To push things further, we can combine some of these symmetries and see whether anything interesting emerges. Take charge and parity (CP) symmetry, for example. Systems that might violate one or other actually end up looking the same if you impose both transformations. In other words, you can find two different perspectives, like a real particle and its antimatter equivalent reflected in a mirror, in which things appear to behave in the same way.

These symmetries matter, largely because we like to see them broken sometimes: the laws, particles and forces of physics all have their roots in symmetry-breaking. They create what David Gross of the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara, calls the “texture of the world”. These considerations have led Florian Goertz at the Max Planck Institute for Particle and Astroparticle Physics in Heidelberg to propose the existence of a new particle that is single-handedly capable of cleaning up five of the stickiest problems in physics. “Complete symmetry is boring,” says Goertz. “If symmetry is slightly broken, interesting things can happen.”

Read more: https://www.newscientist.com/article/mg23931910-200-this-one-particle-could-solve-five-mega-mysteries-of-physics/#ixzz65gUsypha

Links

• Reich HJ & Hondal RJ 2016, "Why nature chose selenium", ACS Chemical Biology, vol. 11, no, 4, 821-841, doi:10.1021/acschembio.6b00031
• Schirber M 2012, "The cosmic history of life-giving phosphorus", Live Science, August 24

Nonmetal table

H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po Rn Ra                                                                                                                                                 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Ac Th Pa U Np Pu Am Cm Bk Cf Es