Question

State Fajan's rule and give suitable example
(4 marks question)​

Answer 1

Fajan’s rule

Fajans’ rule predicts whether a chemical bond will be covalent or ionic. A few ionic bonds have partial covalent characteristics which were first discussed by Kazimierz Fajans in 1923. At that time with the help of X-ray crystallography, he was able to predict ionic or covalent bonding with the attributes like ionic and atomic radius.

What is Fajans’ rule?

We classify certain compounds as ionic and other compounds as covalent. Now if we were to ask, amongst the alkali chlorides, which is the most ionic? To answer these kinds of questions, we employ Fajans’ rules as a tool.

Polarising power

It is the extent to which a cation can polarise an anion. It is proportional to charge density. Charge density is the ratio of charge to volume. Polarising power α Charge density. More the charge density, greater is the polarising power for that cation.

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