Question

Describe Fajan’s rule.

Answer 1

1. The ability of a cation to polarise an anion is called its polarising ability and the tendency of an anion to get polarised is called its polarisibility. The extent of polarisation in an ionic compound is given by the Fajans rule.
2. To show a greater covalent character, both the cation and anion should have a high charge on them. Higher the positive charge on the Cation greater will be the attraction on the electron cloud of the anion.Similarly higher the magnitude of negative charge on anion, greater is its polansability. For example, Na⁺ < Mg²⁺ < Al³⁺, the covalent character also follows the order – NaCI < MgCl₂ < AICI₃
3. The smaller cation and larger anion show greater covalent character due to the greater extent of polarisation. e.g., LiCl is more covalent than NaCI.
4. Cation having ns²np⁶nd¹⁰ configuration shows greater polarising power than the cations with ns²np⁶ configuration. e.g., CuCI is more covalent than NaCl.