Fourth ionization energies

The most stable and common oxidation state of Ln is +3. The principal reason is that the fourth ionization energy I4 of a rare-earth atom is greater than the sum of the first three ionization energies (/1 + h + 3), as listed in Table 18.1.2. The energy required to remove the fourth electron is so great that in most cases it cannot be compensated by chemical bond formation, and thus the +4 oxidation state rarely occurs. 

Write down an equation representing the fourth Ionization energy of beryllium (Be). Is there a fifth Ionization energy ... 

Write equations that show the process for (a) the first two ionization energies of lead and (b) the fourth ionization energy of zirconium. 

The first, second, third, and fourth ionization energies and the standard electrode potential... 

In fig. 4 the first to fourth ionization energies of the lanthanides and actinides are plotted for comparison. It is evident that the half-filled shell effect is much less significant for the actinides than for the lanthanides. This diminished effect is caused by the greater radial extension of the 5f orbitals compared to the 4f orbitals and manifests itself in the easier accessibility of 4-1- oxidation states of many actinides. 

To illustrate how the third and fourth ionization energies dominate the energetics of f-element oxidation-reduction processes, three cycles will be considered. Only the first cycle, scheme I, includes f d transitions inherent in the sublimation of metals. Scheme I represents the process of oxidation of the metal to the normal 3 -i- oxidation state. 

The lanthanide series involves the sequential filling of the 4f electronic shell where the ions exist primarily in the -1-3 oxidation state. The dominance of the 4-3 oxidation state across the lanthanide series is a consequence of the fourth ionization energy being greater than the sum of the first three combined Variable Valency. Shielding from the filled... 

Element First ionization energy/kJ mol Second ionization energy/kJ mol Third ionization energy/kJ mol Fourth ionization energy/kJ mol" ... 

Energy position of the 4f level in the 8. Fourth ionization energies of the Ian- ... 

Fig. 5. Experimental XPS data (Lang et al. 1981) for the position of the 4f level relative to the Fermi energy. For cerium the data point by Platau and Karlsson (1978) is used. These experimental data are denoted by open squares. The filled circles are the calculated values for AEimy (Johansson 1979) (including the zl(n) correction). For ytterbium the dotted square is used to show that this is not an experimental value but is derived from its fourth ionization energy, as described in section 8.

Fig. 9. Estimation of the fourth ionization energy of the lanthanides. Filled circles correspond to experimental values (Martin et al. 1978). The smooth curve is the interpolated D function discussed in the text.

Derived values of the fourth ionization energy for the lanthanide elements by use (4 XPS data from the metallic state. For comparison earlier estimations are given in the last column. (All energies are given in eV). 

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