Question

Give reason:

(a) Cerium(Ce) exhibits $+4$ oxidation state.

(b) Actinoid contraction is greater from element to element than lanthanoid contraction.

Answer 1

a. The electronic configuration of Ce is $\left[Xe\right]4f^{2}5d^{0}6s^2$.

Ce loses 4 electrons to form $C{e}^{4+}$.

The electronic configuration of $C{e}^{4+}$ is $\left[Xe\right]4f^0$

Thus, $C{e}^{4+}$ attains electronic configuration of nearest noble gas Xe. Octet is completed in $C{e}^{4+}$.

Hence, cerium(Ce) exhibits +4 oxidation state.

b. Actinoid contraction is greater from element to element than lanthanoid contraction due to poor shielding of 5f electrons (in actinoids) as compared to shielding of 4f electrons (in lanthanoids). Due to this,the valence electrons of actinoids experience greater effective nuclear charge than that in lanthanoids.

Due to this, the contraction in size is greater for actinoids than for lanthanoids.