Question

what do fajans rules say

Answer 1

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The trend of attaining covalent character by ionic compounds as a consequence of polarisation may be generalized in terms of Fajan's rule.

According to this rules an ion will be formed most easily when

1 .The electron structure of the ion is stable,

2.The charge on the ion is small,
3.A small atom forms the anion and a large atom forms the cation.

If these conditions are not fullfiled, covalent character will develop in the compounds concerned. Thus, increased covalence is favoured by
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1.High charge on the ions,
2.Small size of the cation and large size of the anion
3.Cations with 18-electron structures (i.e., 'non inert gas' type; e.g., Cu+).
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High charge and small size of the cation imparts greater polarizing power to it. Similarly, the electron cloud of an anion is more diffuse when its charge or size is large. This makes the anion easily polarizable.

Answer 2

it is use to predict the type of bond which bond is covelent or ionic bond it is depend on the charge on cation and anion and relative size of cation and anion