Question

How do lanthanoid contraction affect the following property of the elements placed after lanthanoids?

Atomic and ionic radii.

Answer 1

1. Lanthanoid contraction causes a steady decrease in atomic and ionic radii across the lanthanoids due to ineffective shielding by 4f electrons and increasing nuclear charge.
2. This contraction continues to affect elements after lanthanoids, resulting in their atomic and ionic radii being smaller than expected.
3. For example, elements like Hf, Ta, and W have radii very close to their lighter homologs Zr, Nb, and Mo, respectively, cancelling the usual increase in size down a group.
4. Consequently, these elements have almost the same size and similar chemical properties, making their separation difficult.

Thus, lanthanoid contraction leads to smaller atomic and ionic radii for elements following the lanthanoids than predicted by normal periodic trends.