Question

To what extent do the electronic configurations decide the stability of oxidation states in the first series of the transition elements. Illustrate your answer with examples.

Answer 1

If an orbital is half-filled or completely filled, it imparts stability to an atom or ion.

e.g., (1) ${}_{25}Mn=\left[Ar\right]3d^{5}4s^2$

$M{n}^{2+}=\left[Ar\right]3d^5$ (Most stable)

$M{n}^{3+}=\left[Ar\right]3d^4$

$M{n}^{4+}=\left[Ar\right]3d^3$

e.g., (2) ${}_{29}Cu=\left[Ar\right]=3d^{10}4s^1$

$C{u}^{+}=\left[Ar\right]3d^{10}$ (Most stable)

$C{u}^{2+}=\left[Ar\right]3d^9$

In manganese, $M{n}^{2+}$ ion is more stable due to symmetry and half-filled d-orbitals. In the same way in copper, $C{u}^{+}$ ion is more stable due to symmetry and completely filled d-orbitals.