Question

What is the ability of an anion to undergo distortion called?

Answer 1

Fajans rule states that if two oppositely charged ions are brought together, the nature of the vend between them depends upon the effect of one ion on the other.

Complete answer:
Fajans rule states that if two oppositely charged ions are brought together, the nature of the vend between them depends upon the effect of one ion on the other.
Although the bond in an ionic bond is completely ionic but it won’t be hundred percent ionic, it will have some covalent nature in it. When two charges of opposite nature approach each other, the cation starts attracting electrons due to opposite charges, present in the anion but repels its positively charged nucleus.
This results in a distortion or change in shape or polarisation. If the degree of polarization is small then it is an ionic bond and when the polarization of the bond is large it is a covalent bond.
The polarizing power and polarizability which helps in the formation of covalent bond are as follows: -
Small cation - when their higher power in a small area then the polarizing power is high.
Large anion- when the anion is large then they are far away from the nucleus and therefore have weak forces between them and they are lossy held therefore making them easier for them to get polarized.
Large charges- as the charges increases, so increasing the power of cation to polarize
The ability of an anion to undergo distortion is called polarization.

Note:
Large cations are present on the bottom left of the periodic table and small anions on the top right. The greater the charger, the smaller the anion.