Fajan rule

Fajan's rule : 1) Greater the charge on anion or cation, greater is the polarasibility of anion and greater is the polarising power of cation.

2) Smaller is the size of cation, greater is its polarising power.

3) Greater is the size of anion, greater is its polarasibility.

4) Greater polarising power and greater polarasibility induces higher non polar character in an ionic bond.  

                                                                       https://youtu.be/O3D2belxKBs