JEE Main · 2008 · 27 Apr 2008 · Offline · d and f Block Elements

Larger number of oxidation states are exhibited by the actinoids than those by the lanthanoids, the main reason being

(A) $4 f$ orbitals more diffused than the $5 f$ orbitals
(B)lesser energy difference between 5f and 6d than between 4f and 5d orbitals✓ Correct
(C)more energy difference between 5f and 6d than between 4f and 5d orbitals
(D)more reactive nature of the actinoids than the lanthanoids

Answer: (B)

Solution

Actinoids display a wider range of oxidation states than lanthanoids because the

5 f

and

6 d

levels lie close together in energy, closer than the

4 f

and

5 d

levels do in the lanthanoids. With that smaller gap the

5 f

electrons are much more readily drawn into bonding alongside the

6 d

and

7 s

electrons, so a variety of oxidation states becomes accessible, whereas the larger

4 f

5 d

separation keeps the lanthanoid

4 f

electrons largely out of bonding.

JEE Main · 2008 · 27 Apr 2008 · Offline · Single correct option