Question

Give explanation for each of the following observations:

(a) Mn³⁺ is an oxidizing agent, whereas Cr²⁺ is a reducing agent (both d⁴ configuration).

(b) Actinoid contraction is greater than lanthanoid contraction.

(c) Transition metals form interstitial compounds with H, B, C, N.

Hint:

Remember: Stability trends of oxidation states depend on electron configuration and shielding effect.

Answer 1

(a) Mn³⁺ is an oxidizing agent, whereas Cr²⁺ is a reducing agent (both d⁴ configuration).

Mn³⁺ readily gains an electron to become the more stable Mn²⁺, hence acts as an oxidizing agent. Cr²⁺ loses an electron to form Cr³⁺, which is more stable due to half-filled t_2g orbitals (d³), thus acts as a reducing agent.

(b) Actinoid contraction is greater than lanthanoid contraction.

Actinoids have 5f orbitals that are more diffused and poorly shielded compared to 4f orbitals in lanthanoids. This leads to a greater effective nuclear charge and stronger contraction across the series.

(c) Transition metals form interstitial compounds with H, B, C, N.

Transition metals have vacant d-orbitals and lattice voids where small atoms like H, B, C, N can fit without disturbing the structure, forming interstitial compounds which are hard and have high melting points.