Lanthanide elements group trends

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. 

Obvious analogies between Mg and the elements of the 2nd group (notably with Ca) exist. Notice, however, the different behaviour shown in the alloys with the lanthanides and actinides no compound formation is observed with Ca (and Sr, Ba, Eu and Yb) whereas there are several compounds in the alloys with Mg (and Be, Zn, Cd and Hg). As for the patterns given by Zn, Cd, Hg notice the smooth changes along the Periodic Table of the regions where there is, or there is not, compound formation the trend observed in the (sub) group Zn, Cd, Hg is not very different... 

These are listed in Table 2.3 and shown in Figure 2.4. It will be seen that the atomic radii exhibit a smooth trend across the series with the exception of the elements europium and ytterbium. Otherwise the lanthanides have atomic radii intermediate between those of barium in Group 2A and hafnium in Group 4A, as expected if they are represented as Ln + (e )3. Because the screening ability of the f electrons is poor, the effective nuclear charge experienced by the outer electrons increases with increasing atomic number, so that the atomic radius would be expected to decrease, as is observed. Eu and Yb are exceptions to this because of the tendency of these elements to adopt the (+2) state, they have the structure [Ln +(e )2] with consequently greater radii, rather similar to barium. In contrast, the ionic radii of the Ln + ions exhibit a smooth decrease as the series is crossed. 

Niobium (formerly called columbium) and tantalum are Transition Metals having a considerable affinity for oxygen donor groups they are thus called oxophilic see Oxophilic Character). They occur as mixed-metal oxides such as columbites (Fe/Mn)(Nb/Ta)206 and pyrochlore NaCaNb206p. Their discovery in minerals extends back to the beginning of the nineteenth century, when they were believed to be identical and called tantalum. Rose showed that at least two different elements were involved in the minerals, and named the second one niobium. Their separation was resolved around 1866, especially by Marignac. These metals often display similar chemical behavior as a result of nearly identical atomic radii (1.47 A) due to the lanthanide contraction see Periodic Table Trends in the Properties of the Elements)... 

The chemistry of transition metals, lanthanides and actinides is significantly influenced by relativistic effects. Qualitatively, these effects become apparent in the comparison of certain structural properties or reactivity patterns for a group of metals, for example, trends in the chemistry of copper, silver and gold. Quantification of relativistic effects can, however, only be achieved by relating the experimental findings to the results of adequate ab initio studies. Reference to theory is required because nonrelativistic properties cannot be probed directly. Thus, elements behave relativis-tically in any kind of experiment, whether one deals with the spectrum of Hj or the properties of transuranium compounds. 

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