Question

Why do lanthanoids exhibit variable oxidation states?

Answer 1

1. Lanthanoids mainly show +3 oxidation state, but +2 and +4 states are also possible for some elements.
2. The variation arises due to the energy differences between 4f, 5d, and 6s electrons in their electronic configuration.
3. The +3 state is most stable because the sum of ionisation and lattice energies is more favorable for tripositive ions.
4. +2 states occur when lanthanoids lose two electrons, often in elements like Sm, Eu, and Yb; these are less common and usually strong reducing agents.
5. +4 states occur in a few lanthanoids like Ce, Pr, Nd, Tb, and Dy; these states are less stable and usually strong oxidizing agents.
6. The stability of these oxidation states depends on electron configuration, especially the half-filled or fully filled 4f subshell configurations.

Thus, variable oxidation states in lanthanoids are due to their electronic configurations and energy considerations involving ionisation and lattice energies, allowing some flexibility beyond the common +3 state.