Question

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

Answer 1

Answer :-

When a cation of higher valency is added as an impurity, positive charge increases, i.e., two or more than two cations of lower valencies are replaced by less than two ions of higher valencies. To maintain electroneutrality, some cations of lower valency will leave the crystal.

For example, When $Sr^{2+}$ added to NaCl, each $Sr^{2+}$ replaces two $Na^{+}$ ions and then it occupies the site of one ion and the other site remains vacant.

Answer 2

Answer:

When a cation of higher valence is put in an ionic solid, it starts replacing cations of lower valency such that the crystal remains electrically neutral. Thereby, creating some vacant sites. For instance, if Sr2+ is put in NaCl, each Sr2+ ion replaces two Na+ ions. Thereby creating one vacant for every Sr+ ion introduced.