Please explain Fajan's rule clearly with some examples

Applications of Fajan's Rule

(1) Melting point

(2) Diagonal relationship

Berylium and boron resembles with aluminium and silicon. The diagonal relationship observed between the following pairs of elements can be explained with the help of Fajan's rules.

The polarizing power will also increase as the charge over cation increases from left to right in periodic table. In a vertical group, with the increase power of the cation will correspondingly decrease.

(3) Non- polar character and colour

  Colour deepening capacity   polarization of anion

(i) The oxides of colourless cations are usually white but the corresponding sulphides are likely to be deeply coloured if the cation is one which has a tendency to polarize anions. With a few exceptions, the white metal sulphides are only those of alkali and alkaline earth metals.

(ii) In a series of halides of ions such as fluorides and chlorides are colourless ions is usually an indication of an appreciable amount of nonpolar character or some other unusual structural feature. An appreciable amount of polarization leads to intense absorption bands.