Post-lanthanide elements

Lanthanide contraction effects the properties of post lanthanide elements (elements of third transition series). For example,... 

The computational bond-length variations in Table 4.53 exhibit the expected periodic trends. Most noticeably, third- and second-series elements for groups 4, 6, and 10 exhibit similar bond lengths, i.e., the post-lanthanide contraction with respect to the ordinary increase of atomic size with increasing Z. 

The effects of the lanthanide/actinide contraction on the post-lanthanide/actinide main group elements have been investigated by Bagus et al. and Seth et al., respectively. The latter show that the interpretation of the observed total effect in terms of shell-structure and relativistic effects is dependent on the order in which these contributions are taken into account, i.e., a nonadditive behavior is observed (Figure 6). 

The lanthanide contraction, however, has also effects for the rest of the transition metals in the lower part of the periodic system. The lanthanide contraction is of sufficient magnitude to cause the elements which follow in the third transition series to have sizes very similar to those of the second row of transition elements. Due to this, for instance hafnium (Hf ) has a 4" -ionic radius similar to that of zirconium, leading to similar behavior of these elements. Likewise, the elements Nb and Ta and the elements Mo and W have nearly identical sizes. Ruthenium, rhodium and palladium have similar sizes to osmium iridium and platinum. They also have similar chemical properties and they are difficult to separate. The effect of the lanthanide contraction is noticeable up to platinum (Z = 78), after which it no longer noticeable due to the so-called Inert Pair Effect (Encyclopedia Britannica 2015). The inert pair effect describes the preference of post-transition metals to form ions whose oxidation state is 2 less than the group valence. 

FIGURE 1.9 Pre-Seaborg (a) and post-Seaborg (b) periodic tables. RE denotes rare earth elements from 57—71 inclusive LA, lanthanides Z = 57—71) AC, actinides beginning with Z = 89, where Z is atomic number. 

Metals alkali metals (group 1 elements), alkaline earth metals (group 2 elements), transition metals (groups 3 to 11), post-transition metals (group 12 elements and Al, Ga, In, Tl, Sn, Pb, Bi), lanthanides and actinides... 

Cation exchange chromatography in combination with a post-column deriva-tization is also suitable for analyzing uranium and thorium [38]. Because they are actinides and in close relation with lanthanides, they are always associated with them. Due to the lack of simple and sensitive colorimetric methods, the trace analysis of these elements represents a challenge. Although alternative analytical methods for these elements such as neutron activation analysis [39] and ICP-MS [40] are described in literature, they are not suitable for routine analysis... 

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