about fajan's rule ??
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Answer:
Hey mate....
Fajans' rules (note the difference) were formulated in 1923 by Kazimierz Fajans.
They are a method for predicting ionic vs. covalent that predates electronegativity (by three decades) and make use of ionic and atomic radius data that was becoming available through x-ray crystallography.
To use Fajans' Rules, assume your binary compound is ionic and identify the potential cation and anion.
By Fajans' Rules, compounds are more likely to be ionic if: there is a small positive charge on the cation, the cation is large, and the anion is small. For example, NaClNaCl is correctly predicted to be ionic since Na+ is a larger ion with a low charge and Cl- is a smaller anion.
Compounds are more likely to be covalent if: there would be a large positive charge on the cation, the cation would be small, and the anion would be large. For example, AlI3 is correctly predicted to be covalent since it would have a small cation with a high charge and a large anion.
Note that Fajans' Rules have been largely displaced by Pauling's approach using electronegtivites. However, the remnants of Fajans' Rules are found in Hard-Soft Acid-Base Theory, which predicts bonding properties based on polarizability (which is based on size and charge). Binary compounds having a soft acid and/or a soft base are often covalent.
Hope it helps you!!!
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