Talk:D-block contraction

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This sort of behaviour is common to the first shell of every angular momentum, which have no radial nodes. The 4f contraction is famous; the 3d contraction is discussed here; and there is even a kind of 2p contraction that you see in the s-block (Li/Na; Be/Mg). Double sharp (talk) 15:44, 4 July 2016 (UTC)[reply]

if we're going to keep this title...

It should be noted that such contractions across transition series – no, across the whole periodic table – are not at all unusual. They occur in every row in the periodic table and no one is surprised since first-year chemistry that the covalent radii drop logically from Li to F, or from Na to Cl. Likewise in the d-block, ionic radii decrease by 20.5 pm cumulatively from Sc³⁺ to Cu³⁺ and by 15 pm from Y³⁺ to Ag³⁺. The important thing about the 3d and 4f contractions is their magnitude, which is significantly higher than for 4d and 5f (at least until you get to the end of the actinide series when relativity throws a spanner into the works). The lanthanide contraction is in particular the most important here because it is only there that you see the gradation of properties, because it is only there that you have an uninterrupted string of fifteen elements, lanthanum's fourteen twins, that all display the +3 oxidation state as their main one, unlike my previous examples with the unlikely species Cu³⁺ and Ag³⁺. The other reason is that the 3d and 4f contractions are of a large enough magnitude that they significantly cancel out the otherwise-expected increase in size and basicity down the table. One looks at Zr being larger than Ti, and so one would expect Hf to be larger than Zr, except that across the lanthanide series, the shrinking from La to Lu is almost exactly the same amount. Thus, ~~after the chemically odd group 3 which precedes the lanthanides, groups 4 to 8~~ groups 3 to 8 all have the first-row transition metal looking up to her two big twin sisters (ignoring the transactinides which nobody cares about to a first approximation). It is only by group 9 that cobalt contrasts much less with rhodium and iridium, and the latter two do not always act as one (for example, Ir shows the +4 oxidation state readily while Rh does not), and by group 10 Pd and Pt are no longer twins. Finally we get to group 11 with three completely distinct personalities, and then finally group 12 with Zn and Cd being the twins and Hg being the outlier, showing how the effects of the lanthanide contraction have now been completely overshadowed in everything but the metallic radii. The same sort of thing is going on here, so that the 3d contraction (more so than the 4f contraction) does not so much illuminate the properties of the 3d elements, but those of the 4p elements immediately after them. Double sharp (talk) 08:30, 3 November 2016 (UTC)[reply]

Corrected my old comment (group 3 comes after the Ln, according to a proper understanding of anomalous configurations). Double sharp (talk) 08:42, 3 February 2021 (UTC)[reply]