The maximum oxidation state shown by a p-block element is equal to the total number of its valence electrons. i.e., the sum of its s-and p-electrons which is the same as the old group number. In addition to the usual oxidation state, some p-block elements also show another oxidation state, which differs form the group oxidation state by a step of two. A list of elements which show this behavior is given below. These elements occur in the form of following captions: In⁺, Ti⁺, Sn²⁺ and Te²⁺. The greater stability of lower 

oxidation states (than the group oxidation state) of the heavier p-block elements is explained in terms of inert pair effect. The formation of these ions involves the removal of only p-electrons. The two s-electrons remain a party of the inner core of the electrons and are termed an inert pair. (i) One of the explanations offered for the inert pair effect refers to the penetration of the outer s-electrons in the 18 electron shell which is immediately preceding them. They are, therefore, nearer the nucleus and are more strongly held by the atom. Consequently the energy required to ionize these s-electrons is very high and it cannot be compensated by the energy which may be released when two additional bonds are formed. Therefore, this pair of s-electrons in heavier p-block elements does not take part in bond formation and acts as a part of the inner core.

(ii) Another explanation which has been offered for this effect refers to the decrease in the covalent bond forming ability of heavy elements due to a decrease in the strength of their covalent bonds. Thus as the size of the atom increases, its valence electrons get farther away from the nucleus and so their effective overlap and hence the strengths of their bonds decreases.

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