How can an ionic bond have partial covalent in character? I was going through the topic of 'ionic bond' and read this:


  No bond is 100% ionic in character. It has some percentage of covalent character.


I didn't understand how an ionic bond can be partially covalent in character. Please explain along with an example.
One way is Polarization. When a small cation approaches a large  anion it distorts the charge density towards itself thereby forming a type of bond which has directional characteristic i.e from ** (-) ----> (+) ** which is characteristic of a covalent bond.

This polarization has some rules given by **Fajan ** 


Smaller the cation better distortion/polarization.
More the amount of positive charge more is the polarization.
or more the charge : radius ratio of cation more is the polarization.


So in short every cation has the power of polarization and therefore no bond is 100% ionic.