Oxidation state

The +3 oxidation state is common to all the elements, in which the 2 electrons of the s- subshell and one from the d or f- subshell are removed. The 4f electrons are strongly screened by the inner 5s and 5p electrons; thus the 4f electrons are not involved in the bonding. Besides these, some lanthanoids show oxidation states +2 and +4. They are formed in the case of $\mathrm{f^{\,0}}$, $\mathrm{f^{\,7}}$ and $\mathrm{f^{\,14}}$ configurations of the resulting ions.

For example : $\mathrm{Ce^{4+}}$ ($\mathrm{f^{\,0}}$) ; $\mathrm{Eu^{2+}}$ and $\mathrm{Tb^{4+}}$ ($\mathrm{f^{\,7}}$) ; $\mathrm{Yb^{2+}}$ ($\mathrm{f^{\,14}}$). Refer Table 8.11. …