Explain how vacancies are introduced in an ionic solid when a cation of higher valence is added as an impurity in it.

Explanation

Two or more cations of lower valency are replaced by a cation of higher valency to maintain electrical neurality . Hence, some cation vancancies are created. For example , if in the ionic solid, ` Na^(+)Cl^(+) `, impurity of ` Sr^(2+)` is added (as ` SrCl_(2)` ) two ` Na^(+)` lattice sites will become vacant and one of these will be occupied by ` Sr^(2+)` ion and the other will remain vacant.