Question

Give explanation for each of the following observations:

(a) With the same d-orbital configuration (d⁴), Mn³⁺ ion is an oxidizing agent whereas Cr²⁺ ion is a reducing agent.

(b) Actinoid contraction is greater from element to element than that among lanthanoids.

(c) Transition metals form a large number of interstitial compounds with H, B, C, and N.

Hint:

Oxidation states, shielding effects, and interstitial sites are crucial in understanding transition and inner-transition metal chemistry.

Answer 1

Solution:

(a) Mn³⁺ has a greater tendency to gain an electron to attain the more stable Mn²⁺ state. Cr²⁺, on the other hand, tends to lose an electron to become Cr³⁺, which is more stable. Thus, Mn³⁺ acts as an oxidizing agent while Cr²⁺ acts as a reducing agent.

(b) In actinoids, the 5f orbitals extend more into space and are less shielded, resulting in greater contraction in atomic size across the series as compared to the 4f orbitals in lanthanoids, which are better shielded.

(c) Transition metals have small atomic sizes and high charge densities. They can accommodate small atoms like H, B, C, and N in their interstitial sites, forming stable interstitial compounds that retain metallic properties.