Question

What is Fajan’s rule? Discuss.

Answer 1

As we know, a metal combines with a nonmetal through the ionic bond. The compounds so formed are called ionic compounds. A compound is said to be ionic when the charge of the cation and anion are completely separated. But in 1923, Kazimierz Fajans found, through his X-Ray Crystallographic studies, that some of the ionic compounds show covalent character. Based on this, he formulated set rules to predict whether a chemical bond is ionic or covalent. Fagan's rules are formulated by considering the charge of the cation and the relative size of the cation and anion.

1. When the size of the cation is small and that of the anion is large, the bond is of a more covalent character.
2. The greater the charge of the cation, the greater will be the covalent character.