Question

Of the \( d^4 \) species, Cr\(^{2+}\) is strongly reducing while Mn\(^{3+}\) is strongly oxidizing.

Hint:

- Stable electronic configurations drive oxidation/reduction tendencies. - Cr\(^{2+}\) prefers oxidation to \( d^3 \), Mn\(^{3+}\) prefers reduction to \( d^5 \).

Answer 1

Cr\(^{2+}\) is strongly reducing because it tends to oxidize to the stable \( d^3 \) configuration in Cr\(^{3+}\), while Mn\(^{3+}\) is strongly oxidizing as it prefers to reduce to the more stable \( d^5 \) configuration in Mn\(^{2+}\).
Electronic Configurations - Chromium (Cr): \[ \text{Cr}^{2+} = [\text{Ar}] 3d^4 \] \[ \text{Cr}^{3+} = [\text{Ar}] 3d^3 \quad (\text{Stable t}_{2g}^3 \text{ configuration}) \] - Manganese (Mn): \[ \text{Mn}^{3+} = [\text{Ar}] 3d^4 \] \[ \text{Mn}^{2+} = [\text{Ar}] 3d^5 \quad (\text{Stable half-filled d}^5 \text{ configuration}) \] Explanation - Cr\(^{2+}\) loses an electron easily to form Cr\(^{3+}\) (stable \( d^3 \)), making it a strong reducing agent. - Mn\(^{3+}\) readily gains an electron to form Mn\(^{2+}\) (stable \( d^5 \)), making it a strong oxidizing agent.