Lanthanoid contraction

For brevity, the material will be presented in reaction schemes and tables. As far as possible, the dyads Ru/Os, Rh/Ir, Pd/Pt, and Ag/Au will be treated together. The homology of these pairs is expected due to the fact that the size of the two respective ions is very similar (lanthanoid contraction ). 

The Post Transition Metal Effect, Lanthanoid Contraction and... 

It was also proposed that the significant s and p orbital contraction at row four (Cu) is caused by the post-transition metal effect (d contraction), caused by an increase of the effective nuclear charge for the 4s electrons due to filling the first d shell (3d). A similar interpretation is possible for the row six (Au). This effect is commonly called lanthanoid contraction due to the effect of filling the 4f shell. The traditional explanation for the smaller size of gold (compared to Ag) is the lanthanoid contraction. However, this effect is only sufficient to cancel the shell-structure expansion, to make Au (nonrelativistic) similar to Ag (nonrelativistic). 

The values of Vetai listed in Table 5.2 refer to 12-coordi-nate metal centres since not all metals actually adopt structures with 12-coordinate atoms, some values of Vetai have been estimated. The need for a consistent set of data is obvious if one is to make meaningful comparisons within a periodic sequence of elements. Values of Vetai (Table 5.2) increase down each of groups 1, 2, 13 and 14. In each of the triads of the J-block elements, Vetai generally increases on going from the hrst to second row element, but there is little change on going from the second to third row metal. This latter observation is due to the presence of a filled 4/ level, and the so-called lanthanoid contraction (see Sections 22.3 and 24.3). 

This last observation is due to the so-called lanthanoid contraction (the steady decrease in size along the 14 lanthanoid metals between La and Hf see Section 24.3). 

Since much of the chemistries of Cd and Hg are distinct, we shall deal with the two metals separately. In making this decision, we are effectively saying that the consequences of the lanthanoid contraction are of minor significance for the heavier metals of the last group of the J-block. 

Atom and ion sizes and the lanthanoid contraction Spectroscopic and magnetic properties Sources of the lanthanoids and actinoids... 

The lanthanoid contraction is the steady decrease in size along the series of elements La—Lu. 

The Ln ions exhibit large ionic radii ranging from 117 pm for La to 100 pm for Lu, Table 2-1. Also well known, the Ln radii steadily decrease throughout the series as a result of the so-called lanthanoid contraction effect. These are very characteristic chemical features of the lanthanoid elements. 

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