Metallic lanthanides group trends

The trends are similar to those found in halides of the Group I and Group II metals and are explained on an ionic packing model more anions can be packed round the large lanthanide ions early in the series than around the smaller, later ones similarly, more of the small fluoride ions can be packed round a given lanthanide ion than is the case with the much larger iodide anion. 

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. 

The Elecfronic Sfructure of the Lanthanides Variable Valency Group Trends Lanthanides Comparison to 3d Metals Organometallic Chemistry Fundamental Properties. 

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)... 

Two trends are apparent in Table 2.8. Firstly, in going from Sc to to La there is a stepwise increase in radius as principal shells of electrons are added. However, in all of the other groups the increase between the first and second row is not repeated in the second to third row. This is a result of the lanthanide contraction and the filling of the 4f subshell between La and Hf. This reflects the poor screening of 4f electrons one by another, leading to an increase in and a decrease in radius. Secondly, for metals in the same oxidation state, there is a d-block contraction across the rows as a result of the increase in Z... 

There are a number of trends to note. In the well-behaved alkali metals and alkaline earth metals, the radius of an atom increases smoothly as the atomic number increases. The transition metals all have rather similar radii as one passes along the period, and these increase slightly with atomic number going down a group. The same is true for the lanthanides and actinides. 

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