why cant we apply fajans rule to group 1 and 2 elements in deciding solubility

Some ionic compounds r not 100% ionic i;e they have some covalent character in them Fajan stated that when 2 oppositely charged ions approch each other the +ve ion attracts e's present in outermost shell & repels its +vly charged nucleus. This results in polarisation of the anion.The power of cation to polarise anion is known as polarisation power & tendency of anion to get polarised is polarisability. > the pol^ power > itstrndency to form covalent bond.Pol^ power incs with dec in size of the cation & pol'bility incs with inc in size of anion.

eg: LiI has covalent character.