Question

Account for the following :

The $E^\circ_{\text{Mn}^{3+}/\text{Mn}^{2+}}$ value for manganese is highly negative, whereas $E^\circ_{\text{Mn}^{4+}/\text{Mn}^{3+}}$ is highly positive.

Hint:

When studying transition and actinoid metals, pay attention to their oxidation states and how these relate to their chemical reactivity and properties such as melting points.

Answer 1

(I) The highly negative $E^\circ_{\text{Mn}^{3+}/\text{Mn}^{2+}}$ value for manganese indicates that the reduction of $\text{Mn}^{3+}$ to $\text{Mn}^{2+}$ is not favored, as manganese prefers a lower oxidation state. On the other hand, the positive $E^\circ_{\text{Mn}^{4+}/\text{Mn}^{3+}}$ value suggests that the reduction of $\text{Mn}^{4+}$ to $\text{Mn}^{3+}$ is favorable. This is due to the greater stability of higher oxidation states in manganese compared to its lower oxidation states.
(II) Actinoids show a wide range of oxidation states due to the similar energies of their 5f, 6d, and 7s orbitals. This allows for greater flexibility in bonding and more accessible electron transitions, enabling actinoids to exhibit multiple oxidation states.
(III) Transition metals have high melting points due to the strong metallic bonding, which arises from the delocalization of electrons in the d-orbitals. These delocalized electrons form a strong electrostatic attraction between the metal cations and the electron cloud, contributing to high melting points.