Q.Explain the covalent character in ionic bond.

An ionic bond gains partial covalent character when the cation's electric field distorts (polarizes) the anion's electron cloud, pulling some electron density into the space between the ions; this is explained by Fajans' rules.

In a purely ionic bond, the cation and anion would be perfect, undistorted spheres of charge held together only by electrostatic (Coulombic) attraction. In practice, however, the positively charged cation attracts and pulls (polarizes) the outer electron cloud of the negatively charged anion towards itself. This distortion causes some of the anion's electron density to shift into the region BETWEEN the two ions — which is exactly the characteristic feature of a covalent (shared-electron) bond. The greater this polarization, the more covalent character the "ionic" bond acquires.

Fajans' rules describe the conditions that favour greater polarization (and hence greater covalent character) in an ionic bond:

1. Small size of the cation: a smaller cation has a higher charge density and can polarize the anion's electron cloud more strongly.
2. Large size of the anion: a bigger anion has a more diffuse, loosely-held electron cloud that is easier to distort.
3. High charge on the cation (or anion): a more highly charged cation exerts a stronger polarizing field. …