Lanthanide contraction Subject

Hg is much more dense than Cd, because the decrease in atomic radius that occurs between Z = 58 and Z = 71 (the lanthanide contraction) causes the atoms following the rare earths to he smaller than might have been expected for their atomic masses and atomic numbers. Zn and Cd have densities that are not too dissimilar because the radius of Cd is subject only to a smaller d-block contraction. 

For any particular lanthanide, upon subjection to full collapse, the marked drop ( 2 e V) that is incurred in the position of the bottom of the t2g band is coupled intimately with the strong contraction in ag. Firstly, the tZ-function, given its newfound occupancy, becomes more tightly bound, just as for VO2 vs TiO2,... 

Dirac himself dismissed the idea that relativity could impinge on chemistry, he was in fact mistaken, and certainly all the third Transition Series and later elements are subject to its influence. The resulting orbital contraction is additional to the non-relativistic Lanthanide Contraction, and is partly responsible for the close correspondence in sizes between the second and third Series, already noted. It also accounts for the difference in colour and in chemistry between silver and gold, for the unusual structure and weak bonding in mercury, and for many other facets of the chemistry of the heavier elements traditionally associated with the stability of the 6 electron pair.bi2-i8,20-22 electronegative metal, and... 

Binary trihalides RX3 are well known for all rare-earth elements with the exception of Eul3 which appears not to exist due to the relative stability of Eul2- Their crystal structures change subject to the lanthanide contraction within the lanthanide series with high coordination numbers for the lighter lanthanides especially with small ligands (fluoride) and vice versa. Table 1 gives an overview of the crystal structures of the trihalides at ambient conditions. 

Alvarado-Swaisgood and Harrison (1985) found that ScHj has a ground state with = 1.745 A and 0 = 106.7° compared to LaHj which also has a 6 of 106°. The longer La-H bond lengths are excepted since La is neither subjected to lanthanide contraction nor relativistic effects as much as Hf-Au. 

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