Talk:Valence (chemistry)/Archive 1

Archive 1

Valence number or oxidation number?

First. The definition of the valence number given in the article "valence number" is actually the definition of the oxidation number. A valence number must not have a sign; most generally, it is the number of chemical bonds (of any type) that an atom of an element forms in a given substance.

Second. Oxidation numbers vary from -4 (in carbides, etc.) to +8 (in OsO4), but not from -7 to +7! Usually other substances (such as borides, etc.) cannot be correctly described (even formally) using the concept of the oxidation number.

Third. Similar to helium, neon does not form "chemical" (i.e. covalent and/or ionic) substances (or at least I am unaware of such).

Fourth. Unfortunately, I have no time to edit the article right now -- probably later I'll do it.

Fifth. Thank you for reading all this.

Above unsigned comment was added 21:28, 31 January 2006 (UTC) 83.237.103.58

Please merge.

I think it is important to merge valence number with article valency. It would help a lot of other students! Thank you.

• Valence number has now been merged here, as valence is the IUPAC preferred term (not valency). Physchim62 (talk) 01:18, 20 February 2006 (UTC)

Table change

(I didn't know how to edit the chart, so...) If someone else can put all the new data here into a table like before, good.—Preceding unsigned comment added by 74.97.133.196 (talk • contribs)

I have copied the new section to your sandbox (click here), and reverted the edit. Please make clear what you want and what your problems with the current version are. Thank you. --Dirk Beetstra ^{T C} 11:08, 9 December 2006 (UTC)

Simple valence rules vs. modern bonding theory

This comment is for lay people like myself! I studied "A" level chemistry at school in the 1960s and later did a thesis at university in pharmacology. I have been away from science many years. I wanted to refresh my memory about the periodic table and valency. However, I find the dicussion on valency thoroughly confusing. It would be better for lay people like myself to have the simpler things explained and then to give exceptions to this, rather than trying to present the whole thing as a unified theory. It's like explaining Newton's Laws with reference to Einstein. For most intents and purposes the valency of Carbon is 4, Hydrogen 1, Nitrogen 3, Oxygen 2. That gets you through most organic compounds and enables you to understand something about molecular structure. The "noble gases" (Helium, Neon, Argon, Krypton, Xenon)are all basically inert with a valency of 0, apart from certain odd exeptions as you say. Common elements like Sodium and Potassium and Chlorine generally have valency 1 and Calcium and Magnesium 2 etc, while carbonate and sulphate ions act like valency 2 elements and the nitrate ion like a valency 1 element. We know Copper(Cupric, Cuprous) and Iron(Ferric, Ferrous) can commonly have valencies of 3 or 2 and are called transition metals. These sorts of things are what might be relevant to ordinary people.

I would appreciate a clearer explanation of the way electrons and pairs of electrons are involved in covalent bonds and the relevance of the electron shells etc. I remember that I used to be able to predict the valency of an element from its atomic structure and its position in the Periodic Table. I vaguely remember that electrons are "happier"(i.e. more stable) in pairs which can explain why the H2 hydrogen molecule is stable with each hydrogen atom sharing its one electron in a simple covalent bond. This can also explain why elements with complete sets of electrons in their shells(Inert gases) are stable and unreactive. However, how many pairs of electrons can be accommodated in each shell for maximum stability escapes me just now. I've found a good website http://web.jjay.cuny.edu/~acarni/ which I am reading. Thanks for your information. Ggaylmer (talk) 01:02, 11 January 2010 (UTC)—Preceding unsigned comment added by Ggaylmer (talk • contribs) 17:04, 10 January 2010 (UTC)

One problem we have is that valency is considered an obsolete concept; as such, it's not covered much in modern books. Also, it can sometimes be a rather fuzzy concept once you start trying to use electron configurations - which is in fact why it's little used now. But I agree that valence can be a useful concept for understanding basic ideas of what compounds can form and which can't. I can't find the jjay page you're referring to, but I'll see if I can find something to give a basic intro. As for making complete shells, the octet rule article will give you a good overview. Walkerma (talk) 20:13, 10 January 2010 (UTC)

I have renamed this discussion as a new section. Perhaps it would be most useful to compare the two points of view and show where each is useful. We could first note that much of organic chemistry is explained by classical valences which are equivalent to the octet rule, supplemented by the use of resonance structures. Then we can explain that inorganic chemistry includes molecules with hypervalent atoms, transition metals, etc for which the octet rule is insufficient, and point to other articles describing more general bonding theories. Dirac66 (talk) 21:48, 10 January 2010 (UTC)

Thanks for your helpful comments Walkerma and Dirac 66.Ggaylmer (talk) 01:00, 11 January 2010 (UTC). I've hopefully corrected the website detail above, which is from John Jay College, New York and gives a good explanation of electron shells for the lay person. Another good free site is www.visionlearning.com and www.colorado.edu/UCB/AcademicAffairs/ArtsSciences/physics/PhysicsInitiative/Physics2000/

Ggaylmer (talk) 01:27, 11 January 2010 (UTC)

Some references suggested by Gerard Parkin

Prof. Ged Parkin sent me an email with some references which, he thinks, could be used to upgrade this article. Please have a look:

• J. Chem. Educ., 2006, Vol 83, p 791
• A chapter in 'Classification of Organometallic Compounds', 1.01, 2007
• Polyhedron 2004, 23, 2879-2900. doi:10.1016/j.poly.2004.08.004

(He is co-author in all three of them, it seems best that I suggest them here). --Dirk Beetstra ^{T C} 15:23, 1 February 2008 (UTC)

Note: References appear broken on this page. —Preceding unsigned comment added by 122.107.238.251 (talk) 07:32, 4 February 2008 (UTC) yes —Preceding unsigned comment added by Abhiramreddy005 (talk • contribs) 01:18, 28 July 2010 (UTC)

Merge Valence number

Ipendejo largely agree with the comment above and suggest that they can be fixed as part of the proposed merge of Valence number into this article. I support that merge. --Bduke 21:47, 31 January 2006 (UTC)

"Astatine is predicted to have valence of seven but is not known compounds to have any above one", does not make sense! —Preceding unsigned comment added by 86.158.pendejo52.202 (talk) 19:31, 12 December 2010 (UTC)

Fixed. --Bduke (Discussion) 21:48, 12 December 2010 (UTC)

Table change

The valence table is incorrect. Cesium and francium do not have a valence of 3. It would then form compounds without complete outer shells. It is impossible. This is the same for krypton (does not have a valence of 4) and also radon and xenon (does not have a valence of 6). All alkali metals have a valence of 1. All noble gases are unreactive because they have a valence of 0. I don't know of any more corrections to think of. 64.246.250.120 (talk) 16:53, 23 February 2008 (UTC)

No, you are incorrect. Only the gases till argon make inert shells. The others make greater fluorides under liquid air temperatures. It was for this widespread diseducation thas I was banned from Wikipedia for their own mistakes. -lysdexia 03:17, 22 March 2008 (UTC) —Preceding unsigned comment added by 68.123.4.199 (talk)

I must point out that the table should list the valencies under the conditions listed, 0*C and 1 atm. maximum valencies (ie under liquid air,) should be also listed somehow in the table. a "standard" colour code is also recommended, like the one used for resistors (dark grey for black if still using black text) Charlieb000 (talk) 21:34, 3 March 2012 (UTC)

There are many incorrect entries in the table concerning valencies. Valency of all the halogens should be 1. Only Flourine is shown as having valency 1. Other Halogens like Chlorine, Iodine and Bromine also have valency 1. Also some elements like Iron and Copper have multiple valencies. So it is better not to use a colour code for valencies as it gives the misleading impression that valency of an element is unique. — Preceding unsigned comment added by 117.193.176.58 (talk) 06:46, 28 December 2011 (UTC)

Yes, the values in this table are rather arbitrary. There was a long discussion early this year at the talk page for the table - see Template talk:Periodic table (valence)#Delete?. One point is that the colour for each element is not supposed to be a unique value but corresponds to the maximum valence as per the IUPAC definition. The section with the table did use the word "maximum" once at the beginning, but I have now added it three more times for emphasis - once in the section title, once more in the text, and once in the title for the colour code (which required changing Template:Element color legend/valences).

As you say, however, it would be better to eliminate the color code entirely. It could be replaced by a list of the valences for each element, at least in neutral molecules. This would however require rewriting the table completely. Dirac66 (talk) 21:23, 28 December 2011 (UTC)

Maximum valence of Oxygen

The maximum valence of oxygen can be 4, if we regard ozone as oxygen dioxideAnoop.m (talk) 16:48, 1 April 2012 (UTC)

Expert needed

We have recent multiple edits by single user - no edit summaries - without relevant citations , very difficult to track consistency, expert needed to sort things out V8rik (talk) 17:52, 29 December 2010 (UTC)

Interesting article. Unfortunately, "valence" is a concept that has many different meanings to many different people. It is nonetheless a useful concept when properly defined. In many ways, the concept and meaning of "valence" is as complicated and ill-defined as "aromaticity" - perhaps more so. One problem is the the term is a bit too useful and too often employed to cover a multitude of sins. Valency has become one of those terms in chemistry that requires a specific ad hoc definition to be certain that one understands precisely what an author means by its use in a specific situation. In the case, such as in Wikipedia, where one seeks a "general," but nonetheless "precise" and concise definition, there's going to be a problem among multiple authors. Another problem that one faces in defining such a term is the "house of cards" that we've built with many of the terms that we use in chemistry. Many of these terms are too flexibly defined to serve as any good basis for the definition of other terms. Consider, for example, the term "bond." "Bond" is used to provide one of the "definitions" of "valence." However, "bond" also has multiple interpretations, there are after all 2-electron 2-center (common) sigma-bonds; 4-electron 3-center bonds; pi-bonds; 3-center 2-electron bonds (c.f. the section referring to the 3-c,4-e hydrogen bond with a 3-c, 2-e electron deficient diborane H-bond); ionic; usw. Bonds present yet another problem. Valency logically has some sort of connection with "oxidation state," or at least it should. However, to "know" an oxidation state one needs to know where the electrons "are" - not an easy task when electrons don't correlate with the definition of "bond." The more sophisticated one becomes in his or her "understanding" of chemistry, the greater the tendency to believe that one has a superior insight and precise command of the field. Of course if people's perspective and experiences are different the view of definitions used by these individuals will be ever so slightly morphed to conform to one's needs and experiences. Hence, the broad science of chemistry suffers from a drift of definitions with both time and location (subdiscipline). There's a lot to be said for returning to older insights nearer to the original point of introduction of a given term. In the case of "valency," Pauling's "Nature of the Chemical Bond" and "General Chemistry" textbook provide powerful fixed insight into the intent of the term. From that point one can develop a chronological mutation of definition that actually provides an interesting "snapshot" of the state of the art of chemistry at any point in time. Another enormous problem that we face as chemists is our past. Chemistry developed as a descriptive science. We see a phenomenon (reaction or substance) and subsequently describe, define, and categorize what we see. Ketones or aldehydes were originally defined as ketones or aldehydes according to how they react (and what we see) when they react with reagents like 2,4-dinitrophenyl hydrazine. Problems arise when we try to describe things that we cannot see. Put another way, what a substance is, and how it reacts are two different things. Only relatively recently are we able to "look" precisely at the structure of a substance with a minimum of perturbation to that structure. The traditional reaction used to define a substance represents an event (a reaction) that does not take place from the ground state structure of a substance, but rather from some excited state along a reaction surface. Naturally, the excited state of a substance is different from its ground state.

In essence, one needs to define "valence" in terms that have not varied (much) over time. If you haven't already done so, it's well worth having a look at some of the encyclopedic works of Musher and Pauling. Unfortunately, even with a good concise definition, someone else is likely to come along and change the definition because they "need" it to mean something a little different. However, as stated above I find fixed, solid, broadly accepted definition quite useful especially when they are based on "first principles" with which everyone should agree. AJArduengo (talk) 04:05, 30 December 2010 (UTC)

I think the original concept of valence was the number of "bonds" that an element can form, which some chemists (e.g. Frankland and Kekulé in the mid-19th-century?) assumed to be constant. It is true that the valences of Na and C are almost always constant, but chemists later realized that most elements can form varying numbers of bonds, and also that there are different types of bonds, notably ionic and covalent. So the concept of valence fragmented into several related concepts - actual number of bonds, maximum number (IUPAC definition), oxidation state, etc. I think the article should reflect this reality - mention the original vague concept first, and then survey the various modern meanings. We should not pretend that there is still one universally accepted concept of what valence means. Dirac66 (talk) 15:30, 30 December 2010 (UTC)

The many places where "valence" becomes an adjective certainly require a minimum standard definition. Often chemists speak of "valence" shell electrons - that is those electrons that may become involved in bonding (making connections) to other atoms. For paper and pencil chemistry this concept is exceedingly useful and provide some boundaries on the possibilities that one must consider. Beyond the neon atom, the electrons with which must deal are less than those in the sub-valent (inner) shells. As the number of valence shell electrons increases the problems do become more complex, but nature provides some limiting features that restrict the number of reasonable possibilities that one need consider. For the s-block elements with a maximum of only two valence electrons the "valence" possibilities are restricted to schemes in which only (up to) two electrons from the "central" atom need beconsidered; add to this the tendency toward ionic bonding when the elements are highly electropositive and/or have only large diffuse orbitals at their valence shell and the possibilities for covalent (shared electron) bonding is further diminished. Of these s-block elements hydrogen has the best possibility of forming covalent bonds that might be well served by "valency" descriptions. As pointed out in present article, hydrogen also shows 4-electron, valency-2 (coordination number 2) bonding arrangements. These hydrogen bonded (4-H-2) species fall into a category of "hypervalent" (beyond the "normal" valency). Pauling also coined a term for this - "transargononic" (although in the case of hydrogen I suppose the analogous term would be "transhelionic" ;) ). For the p-block elements the valency "limit" that one need consider is 8 with due consideration given to charge buildup (limited in part by Pauling's electroneutrality principle, electronegativity, and diffuse orbital nodal structure (limiting covalent bonds) for the heaviest elements. For the p-block elements "hypervalency" or "transargononic" bonding provide the addon to describe many important structures. For the d-block elements, the convenience limit is 10, but the electropositive nature of most of these elements and the complex nodal structure of d-orbitals limits the extent of truly shared electron bonding in favor of ionic structures. Finally, the f-block elements (which should have a limit of 14) are strongly restricted in bonding types due to the electropositivity of the element and their very complex valence orbital (f-orbital) nodal structures that severely limit overlap with orbitals on adjacent centers and hence shared-electron or covalent bonding. AJArduengo (talk) 02:35, 31 December 2010 (UTC)

• Thanks AJArduengo and Dirac66 for your insights. We can start with Pauling's definition and then describe the evolution of the concept. We will not adopt one of the definitions and then suppress all the others V8rik (talk) 16:29, 31 December 2010 (UTC)

I would like to invite AJArduengo and Dirac66 to share their insights with us discussing the periodic table, which is on a separate page. OneAhead (talk) 03:07, 29 January 2011 (UTC)

"Valenz" is in german simply an umbrella term for the ion charge, the Coordination number, the Oxidation state,... (for a source see the german wikipedia - it provides a source). Maybe in english there is the same problem that "Valence" is an umbrella term?--Biggerj1 (talk) 15:29, 29 July 2013 (UTC)

Multivalent Ion

The term multivalent is used incorrectly in this article. Multivalent refers to elements such as iron that have multiple possible valence states, such as iron (II) in FeO and iron (III) in Fe2O3. I have never heard calcium being referred to as multivalent. It would be correct to define it as divalent, but not as a multivalent particle. I think there should be a specific wikipedia article title multivalent or multivalency. If I had the time to learn how to navigate Wikipedia editing as well as the time to write an article, I would fix the article titled "Valence(chemistry)" and I would create one titled "Multivalent" or "Multivalent Ion". 74.117.253.211 (talk) 16:03, 14 October 2013 (UTC)Pete

Rating

I have re-rated this article as C. It has too many problems to rate B. The quality of the article is dubious, I was struck immediately by the definition of valence in the lede which is the "number of valence bonds a given atom has formed...". Valence as originally couched (19th century; pre-Lewis, yet alone Pauling) was an observable; a simple experimentally verifiable count of the "attachments" an atom of an element could make, and by verifiable I mean using known equivalent weights (19th century definition) and the emerging knowledge of atomic weights. As such, as an observable, it was different and separate from the models that we now use to "explain" it, (e.g. Lewis/Langmuir octets, VB theory, MO theory, hypervalence etc. etc.). I was also amused by the section on oxidation state, related to be sure but replacing valence? IUPAC's oxidation number relates to simple molecules with a central atom, Paulings version, using electronegativity, whcih can be applied to more complex molecules requires a structural formula, with little valence strokes, as the starting point. I could go on. I do not have the time in the forseeable future to work on this, hopefully someone will pick up the gauntlet. Axiosaurus (talk) 12:57, 24 March 2014 (UTC)

Covalent and ionic bonds still confused

This article still confuses covalent and ionic bonds. Worst example - in the paragraph titled Covalence, we learn (in bold type!) that an atom with a +1 valence (one electron beyond the complete shell) and an atom with a -1 valence (requiring one electron for a complete shell), then a bond between these two atoms would result. Sounds like the ionic bond in NaCl to me. And even more so because it is not said that the two atoms must be close to each other. We need to explain clearly that the historic concept of valence corresponds to the TWO concepts of covalent and ionic bonds (plus intermediate cases of course), and point out clearly when we are talking about covalent and when about ionic.

Also in the section Valence versus oxidation state, we learn that in perchlorates, chlorine has seven valence bonds. A high school student could be forgiven for thinking this means that the Cl is surrounded by 14 valence electrons forming 7 Cl-O covalent bonds. Again the partial ionic character of the bonds should be pointed out. Dirac66 (talk) 18:00, 10 April 2014 (UTC)

I think that the problem is that valence (Greenwood calls it a property of an element), a simple count of the connections an atom of an element can make has been intimately mixed in this article with modern bonding concepts and theories. This is the correct article in which to describe the evolution of the valence concept, stemming from the work of Kekule, Couper, Frankland et al, which even now gives a reasonable account, albeit non-geometric, of many molecules in organic chemistry. This is also the right article in which to describe the shortcomings of the concept. I am assembing information on this, albeit slowly, as real life is quite demanding at the moment.

I wonder whether this is the right article to describe the evolution of the "electronic theory of valency" following Faraday, JJ Thomson, Lewis, Langmuir, Bohr, Sidgwick, Schroedinger, London, Pauling, Millikan [Mulliken?], Coulson et al, or to try to describe the current understanding of valence, which is actually a plethora of conflicting and complex theoretical treatments, VB, MO, LMO, hypervalence etc etc. By the way the valence concept treatment of chlorate is excellent- for halogens the group valence minimum is 1 and maximum is 7, chlorates were not confusing at all when I was at high school, 50+ years ago, it only got confusing later! The modern explanations of the bonding in the isoelectronic series of SiO₄^4-, PO₄^3-, SO₄^2-, ClO₄^- are complex, even contentious, and I sympathise with modern high school students, at their stage they need certainties that enable them to pass exams. Axiosaurus (talk) 11:44, 11 April 2014 (UTC)

I think the evolution of the electronic theory of valence would be the best approach. At the moment the article starts this way, and does attempt to separate the concepts of Higgins (1789), Frankland (1852), and Langmuir and Lewis (1919). But then the historical approach is abandoned, and we make no attempt to separate the ideas of Pauling from the results of recent ab initio calculations. Again using perchlorate as an example, you have reminded me that I learned as an undergraduate (also 50+ years ago) that the chlorine forms 7 bonds by sp³d³ hybridization, which was Pauling's description of hypervalence. More recent calculations and theories have gone a long way to restoring the octet rule, but as you say they are complicated.

So to keep this article at a reasonable level, I think we can trace the evolution of the concepts in the pre-ab initio age, and then indicate only briefly more recent conclusions such as the minimal participation of d orbitals in main-group bonding, with links to more detailed articles. Dirac66 (talk) 19:03, 12 April 2014 (UTC)

I have reworded the lede added examples and tidied up the rest a little. Real life prevents a full blown attempt to write a historical narrative at the moment. I am reading around Kekule/Odling views on unsatisfied affinities, and some of the trends e.g. in paramagnetism of metals, that the old timers noted which predate Lewis/Langmuir. The idea of positive and negative valencies was mooted Kossel I think, the +/- covalent/ionic confusion you note in the article may relate to that idea - so for the moment I have left it as is as I haven't got to the bottom of it. Axiosaurus (talk) 17:26, 21 April 2014 (UTC)

I have now extended the historical section which previously stopped with Frankland in 1852! So I have added Kekulé, Werner, Abegg, Lewis, Langmuir (moved from the final section), Pauling and quantum chemical calculations as per Magnusson in 1990. Dirac66 (talk) 21:45, 25 June 2015 (UTC)