Talk:Inert-pair effect

Electron remains in s-orbital?

I've removed the following section because it's unsourced and contradicts my understanding of the inert pair effect:

The inert pair effect can explain why Thallium forms Tl₂O while aluminium in the same group forms Al₂O₃.In aluminium, the electronic configuration is [Ne]3s² 3p_x¹. Because of the screening effect of the 2p electrons, one of the 3s electron can be excited easily to the 3p_y orbital. So Al mostly exhibits a valency of 3. However in case of Tl, the electronic configuration is [Xe]4f¹⁴ 5d¹⁰ 6s² 6p_x¹. Due to the poor screening effect of the 5d orbital, the effective nuclear charge on the 6s electron is high. Hence it cannot be excited to the 6p_y orbital. So the only unpaired electron remains in the 6p_x orbital. Hence Thallium exhibits a valency of 1 and forms Tl₂O. Similar effect is observed in tin and lead.

"Inert pairs" are stereochemically active so it doesn't make sense to me that they'd simply remain within a perfectly spherical orbital. I'm no expert on this so I could be wrong but the section could do with some rewriting anyway. Blackthirteen 00:01, 5 July 2007 (UTC)

The paragraph is wrong, but not for the reason you think it is: if the paragraph were correct, gallium would show a very strong inert pair effect, whereas it shows none at all. The correct explanation involves the effects of special relativity on the mass of the electron: for atoms with a very high nuclear charge, the s-electrons are travelling so fast near the nucleus that the reletivistic increase in mass is non-negligeable, which causes the s-orbitals to shrink and the ionization energy of s-electrons to increase. Physchim62 (talk) 01:02, 2 August 2007 (UTC)

WikiProjects

Shouldn't this also be a part of Wikiproject: Chemistry? Or is there such a thing? RobertAustin 17:32, 26 November 2006 (UTC)

Done. Physchim62 (talk) 01:02, 2 August 2007 (UTC)

WikiProject class rating

This article was automatically assessed because at least one WikiProject had rated the article as stub, and the rating on other projects was brought up to Stub class. BetacommandBot 09:54, 10 November 2007 (UTC)

rewrite- sorry

I initially tried a simple expansion but I have ended up with a complete rewrite. I hope no-one is offended. The only questions I have now is why this topic was ever categorised as a relativistic effect--yes Rel effects matter for the heaviest members but looking at the IPs it is obvious that the inert pair effect is not due to higher energy s electrons. Sadly for us all the name is a misnomer--Sidgwick started it in 1927--great man that he was - but he got this one wrong! In terms of the evolution of chemistry the term inert pair effect is probably best viewed as a vestige left over from a palaeolithic past, a bit like the human appendix. sadly for student chemists the simple explanation of the effect is still being taught, so if anyone gets low marks for quoting this article I'm sorry! Axiosaurus (talk) 18:13, 9 January 2008 (UTC)

abbreviation meaning??

The article Ionization potential doesn't explain the terminology used in the chart. Is "1st" supposed to mean "first" or something else (I assumed "first" until I saw the rest of the chart)? Then what is "2st" -- "second"?? "3d" - "3rd","third" or an orbital? And at last, what does 2^d + 3^d, used several places in the article, mean at all?? "second plus third" ionization potential or some other specific chemical meaning? If it's just "first", "second", "third", use consistent terminology all the way through -- if not the words, then e.g. 1^st, 2^nd, 3^rd, or the same set without the superscripts. If it means something else, explain what it means (either in this article or Ionization potential), or write it out in full, please? - someone who thinks they do know what is meant? Thanks, —Isaac Dupree^(talk) 11:51, 10 July 2008 (UTC)

Corrected the typo - hope that clarifies it! --Axiosaurus (talk) 12:03, 10 July 2008 (UTC)

Groups 12 and 11?

Is this effect confined strictly to groups 13-16? I think the difficulty of oxidation of Hg(0)has also been attributed to the inert pair effect. And also the stability of the auride ion Au(-1). Dirac66 (talk) 20:07, 26 November 2008 (UTC)

You're completely correct: there are several properties of gold and mercury which could be attributed to relativistic effects, of which the inert pair effect is one. However, the term "inert pair effect" is generally used to describe the chemistry of thallium, lead and bismuth, especially the extraordinary oxidizing power of their highest (group) oxidation states. As such, the article as it stands is not wrong, even though it only tells a part of the story. Physchim62 (talk) 22:18, 26 November 2008 (UTC)

The term inert pair effect is historic- Sidgwick 1927. IMO it should never have been called an "effect", it was more an observation. It can be rationalised in terms if ionisation potentials. It describes the increasing stability of an oxidation state 2 lower than the group oxidation state for period 4 and above elements in groups 13-16, and is not restricted to just period 6 elements as Physchim62 (above) seems to be suggesting. Gold and mercury 6s² stability was never seen as the same "effect", although it indubitably is a "pair". In terms of historical authenticity this article is in my view correct- (but I would say that wouldn't I), however the inert pair effect certainly does not tell a good chemistry story these days.

Relativistic effects are important particularly for the heavier elements (See Pyykko's 1988 review http://www.chem.ubc.ca/courseware/320/cr00085a006.pdf (big pdf 4+MB but perhaps a little out of date ) and explain the anomalous 6s² stability noted for Au and Hg, but are not the main reason for d-block contraction and therefore the "inert pair effect" of say gallium traditionally explaining why Ga(I) is more common than Al(I), but are important in lanthanide contraction and therefore relevant to explaining the stability of Tl(I) relative to Tl(III). Perhaps some of Pyykkos points re rel effects on ionisation potentials and orbital contraction could be added to this article and the d-block and lanthanide contraction articles.--Axiosaurus (talk) 14:40, 27 November 2008 (UTC)

Did Sidgwick use the term "inert pair effect" to describe the anomalous chemistry of period 4 elements? After all, he must have realised that perchlorate and periodate existed but that perbromate didn't (first prepared in 1968). Physchim62 (talk) 15:05, 27 November 2008 (UTC)

As far as I know halogens were never included- I am not surprised- group valency 7 and valency 5 would have been the two to compare , e.g.perhalates with halites(XO₄^- with XO₃^-) , application of inert pair effect thinking would predict halites progressively more stable w.r.t. perhalates, and perhalates becoming progressively stronger oxidising agents as go down the group -Doesn't look obvious on a quick visit to modern text books so probably not obvious way back then. And as you observe periodate well known and perbromate a "recent" discovery.--Axiosaurus (talk) 17:34, 27 November 2008 (UTC)

The perbromate example was the one I used to use to illustrate the d-block contraction back in the days that I used to have to teach it. There are others, of course: the great similarity in chemistry between period 3 and period 4 elements in the p-block (the point I was trying to get across by explaining why), and the oxidizing nature of arsenates and selenates (less than that of perbromates, but still noticeable). However, I never thought to call that the "inert pair effect", a term which I reserved for period 6. None of that means I'm right, obviously, but I didn't just make my courses up, I must have had some (possibly subconscious) click from my own chemical studies to present things in that way. Physchim62 (talk) 18:40, 27 November 2008 (UTC)

Looks like I misunderstood your point! I think your students were lucky- I was not, and still bear the scars. d-block contraction, lanthanide contraction and relativistic effects are all an observable electronic effect and therefore in a different category from the inert pair effect which should be relegated to history of science lectures and only taught as an aide memoire. --Axiosaurus (talk) 10:53, 28 November 2008 (UTC)

I seem to have started quite a discussion here. I think that my initial question has been answered, as you both agree that the effects in Au and Hg are relativistic but not identical with the "inert pair effect", and so do not belong in this article. I note that there is a good list in relativistic quantum chemistry, although without explanations.

It also seems clear from the above discussion that the exact list of phenomena which constitute the "inert pair effect" is quite ill-defined, and the theoretical explanations are far from conclusive. Perhaps this should be made clear early in the article.

I think though that this article should be retained in Wikipedia as an important historical concept, even though its inclusion in contemporary inorganic courses is diminishing. After all, Wikipedia even has an article on phlogiston! Dirac66 (talk) 23:23, 28 November 2008 (UTC)

Well it gets even more complicated from a historical perspective! Sidgwick includes mercury in his "inert pair effect", noting the unusual covalency of Hg^I and Hg^II compounds. And he also includes periods 4 and 5, although he notes that the effect is most pronounced in period 6 (and, in general, in group 14).

He remarks on the non-existence of perbromates, but does not explain it by his "inert pair effect": on the other hand, he explains the existance of [I₃]⁻ and [ICl₂]⁻ on the basis of the inert pair effect (what we would now call "expansion of the octet" – see hypervalent molecule), ignoring their similarity with iodonium salts [Ar₂I]⁺. The reason seems to be that there wasn't a formal concept of oxidation state at that time to systematize the various different effects within valency theory… Physchim62 (talk) 11:33, 29 November 2008 (UTC)

To expand on that last point: for Sidgwick, chlorates, bromates and iodates were 3-valent, perchlorates (and some periodates, along with the non-existent perbromates) were 4-valent and most periodates were 6-valent! Hence he says (pp. 291–92): "The other halogens [apart from fluorine] readily assume a covalency of more than one, and do so on the whole with greater ease as the atomic number increases." On this point, he is in agreement with the more complete set of Fajans' rules than we use today. Sidgwick seems to have been a great fan of what he calls "Fajans theory". Physchim62 (talk) 12:01, 29 November 2008 (UTC)