Wikipedia:Reference desk/Archives/Science/2019 June 29
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June 29
[edit]Melting and boiling points of francium and astatine
[edit]Did anyone ever actually measure these, or do we only have predictions? The articles francium and astatine list them all as calculations or estimations in the body, and the At article even mentions that some experimental data suggests that the predictions are wrong. Double sharp (talk) 10:44, 29 June 2019 (UTC)
- Don't know, but it must be a difficult thing to measure, since the actual temperature is difficult to control. This is because the highly radioactive nature of those elements generates more heat in the interior than on the surface, making it difficult to keep a sample at a constant temperature. SinisterLefty (talk) 10:52, 29 June 2019 (UTC)
- I managed to get the text of the paper our astatine article cites for the experimental indications (10.1524/ract.1982.31.34.201): it indeed confirms the difficulty due to radioactive heating, inability to get a large quantity, and boiling point elevation due to polonium impurities that keep getting generated from astatine decay. So it simply gives an estimate based on semi-empirical theory on retention volumes from radio-gas chromatographical experiments (which is, of course, much better than just extrapolating from the halogen trend). As for francium: the closest I have been able to get is this paper, which quotes some estimations from its citres [6] and [7] (with a value of 871 K for the boiling point of Fr that seems more in keeping with the periodic law than the 950 K we currently quote), but I can't find those original sources for them to see if the values therein are just calculated or have any experimental basis behind them as well. Double sharp (talk) 12:28, 29 June 2019 (UTC)
- There are some interesting papers around this locus. Will try to leave them, morrow. ∯WBGconverse 19:19, 30 June 2019 (UTC)
- I managed to get the text of the paper our astatine article cites for the experimental indications (10.1524/ract.1982.31.34.201): it indeed confirms the difficulty due to radioactive heating, inability to get a large quantity, and boiling point elevation due to polonium impurities that keep getting generated from astatine decay. So it simply gives an estimate based on semi-empirical theory on retention volumes from radio-gas chromatographical experiments (which is, of course, much better than just extrapolating from the halogen trend). As for francium: the closest I have been able to get is this paper, which quotes some estimations from its citres [6] and [7] (with a value of 871 K for the boiling point of Fr that seems more in keeping with the periodic law than the 950 K we currently quote), but I can't find those original sources for them to see if the values therein are just calculated or have any experimental basis behind them as well. Double sharp (talk) 12:28, 29 June 2019 (UTC)
With R8R's help I've been trying to track down better figures for Fr at his talk page: we have found some figures (m.p. 8.0 or 20±1.5; b.p. 620 or 640, all degrees Celsius), but I suspect that they are probably predictions (the set 20±1.5/640 is certainly calculated by Mendeleev's method). Double sharp (talk) 04:52, 2 July 2019 (UTC)