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⁺ is more inclined to accept an electron, forming the stable Mn²⁺ state. Conversely, Cr²⁺ tends to lose an electron to achieve the more stable Cr³⁺ state. Consequently, Mn³⁺ functions as an oxidizing agent, while Cr²⁺ acts as a reducing agent.

(b) The 5f orbitals in actinoids extend further and are less shielded than the 4f orbitals in lanthanoids. This leads to a more pronounced decrease in atomic size across the actinoid series compared to the lanthanoid series.

(c) Due to their small atomic radii and high charge densities, transition metals can accommodate small atoms such as H, B, C, and N in their interstitial spaces. This forms stable interstitial compounds that retain their metallic characteristics.