Question

give Fajans rules for the partial covalent character of ionic bonds

Answer 1

Dear Student,

Fajan's rule tells us about the covalent characters present in an ionic bond using the concept of polarisation. Some important points related to Fajan's rule are:

• When cation and anion comes closer to each other for forming an ionic bond, electron cloud of anion is deformed (distorted) by high Zeff of cation and this is known as polarisation.
• Due to this polarisation, covalent characters are generated in ionic bond.
• CATION: more the charge/radius ratio (ionic potential) of cation, more will be the polarising power of the cation will be. It means that the cation having more charge and smaller size, will have high Zeff and it will more easily polarise the anion. This type of bond will have higher covalent character compare to a cation will less charge and large size.
• ANION: Larger the size of anion, more farther the electron cloud from the nucleus and it can be easier to distort by cation (high polarizability). Similarly, high charge on anion, Zeff will be low and there will be decrease in hold on electron cloud by nucleus. Thus easier distortion.
• Therefore an anion with more charge and larger size have high polarizability and thus high covalent characters in ionic bond.

These all factors and rules which provide us a comparison for the presence of covalent characters in ionic bonds are collectively called Fajan's rule.

Regards.