138. How is the variability in oxidation states of transition metals different from that of the non-transition metals? Illustrate with examples.

The variability in oxidation states is a fundamental characteristic of transition elements and it arises due to incomplete filling of d-orbitals in such a way that their oxidation states differ from each other by unity. For example, vanadium, V show the oxidation states of + 2, + 3, + 4 and + 5. Similarly, Cr shows oxidation states of +2, +3, +4, +5 and +6; Mn shows all oxidation states from +2 to +7.
This is contrasted with variability of oxidation states of non-transition elements where oxidation states generally differ by units of two. For example, S shows oxidation states of -2, +2, + 4, +6 while P shows +3 and +5 oxidation states. Halogenes like Cl, Br and I show oxidation states of –1, +1, +3, +5 and +7 states. In non-transition elements variability of oxidation states is caused due to unpairing of electrons in ns or np orbitals and their promotion to np or nd vacant orbitals.