126. 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 example.

One of the main characteristic of a transition element is that it can show large variety of oxidation states in its compounds. It is due to its characteristic electronic configuration i. e., (n – 1)d and ns electrons take part in bond formation either by loosing or by sharing of electrons with other combining atoms.
The stability of oxidation state depends mainly on electronic configuration and also on the nature of other combining atom.
The elements which show largest number of oxidation states occur in or near the middle of series (i.e., 4s²3d³ to 4s²3d⁷ configuration). For example, Mn exhibits all oxidation states from +2 to +7 as it has 4s²3d⁵ configuration. The lesser number of oxidation states at extreme ends arise from either too few electrons to loose or share (e.g. Sc and Ti) or too many d electrons (hence fewer orbitals available in which to share electrons with others) for higher elements at upper end of first transition series (i.e., Cu and Zn). Thus electronic configuration, to large extent, the existence and stability of oxidation states.
The other factors which determine stability of oxidation state are:
(i) Enthalpy of atomisation (ii) Ionisation energy (iii) Enthalpy of solvation (iv) E.N. of other element.