Lanthanides ionization energies

Figure 30.3 Variation with atomic number of some properties of La and the lanthanides A, the third ionization energy (fa) B, the sum of the first three ionization energies ( /) C, the enthalpy of hydration of the gaseous trivalent ions (—A/Zhyd)- The irregular variations in I3 and /, which refer to redox processes, should be contrasted with the smooth variation in A/Zhyd, for which the 4f configuration of Ln is unaltered.

Owing to lanthanide contraction, niobium and tantalum have virtually identical atomic rad (1.47 A) and close ionization energies (Nb6.67, Ta7.3eV), and usually display very similt chemical behavior. Some definite differences can however be noted these can usually be trace to the lower sensitivity of tantalum to reduction and to its higher affinity for dioxygen. lb tantalum-element multiple bonds are usually stabler, while MfiXg arrangements are so ft known only for niobium. 

The ionization energies of lanthanides to yield Ln(III) and Ln(IV) are given in Table 2.8. It is seen from the data that all the ions have a ground state configuration of [Xe]4/n with the exception of La2+ and Gd2+. 

In order to understand the properties of lanthanide compounds of 4/" configuration with the high number of energy levels and the ionization energies for... 

The values of the first four ionization energies for the lanthanides (and yttrium) are listed in Table 2.2. 

Cumulative ionization energies across the lanthanide Series (reproduced by permission of Macmillan from S.A. Cotton, Lanthanides and Actinides, Macmillan, 1991). 

When is it most likely that Ln +(aq) ions will be stable For the first of the two reactions above to be favoured, the single factor that will help make A// positive is a high value of h. Less important would be the size of the ions, as this could affect the hydration enthalpies the difference between the hydration enthalpies will be less, the larger the lanthanide ions. Substituting into the above equation, we can investigate the relative stabilities of La +(aq) and Eu +(aq), making use of ionization energies from... 

Although a full range of ionization energies is not available throughout the actinide series and thus cannot be used predictively, as for the lanthanides (Table 2.2), electrode potentials are more generally available (Table 9.5) and thus can be so used, as follows ... 

Whether an individual lanthanide forms a dihalide depends npon a nnmber of factors, particnlarly the valne of h, the third ionization energy. There are three main types of lower halides. 

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