Question

Discuss Lanthanoid contraction and its effect?

Answer 1

Lanthanoid contraction:
It is the gradual decrease in the atomic and ionic radii ( of lanthanoids) with increase in the atomic number. It is due to imperfect shielding of one electron by another electron in the same 4f subshell. The extent of shielding for 4f electrons is less than that for d electrons as f subshell has diffused shape.
The gradual decrease in the atomic and ionic radii of lanthanoids is very small.
Effects of lanthanoid contraction:
(1) The basic character decreases from $L{a}^{3+}$ to $L{u}^{3+}$. Thus, $La(OH{)}_3$ is more basic than $Lu(OH{)}_3$.
(2) The atomic/ionic size of post lanthanoids is similar to that of the elements of previous period.
Thus, $Hf$ and $Zr$ have almost similar atomic radii. Similarly, $Ta$ and $Nb$ have almost similar atomic radii.