Q.Describe Fajan's rule.
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Start your 14-day free trial to unlock the full solution →Step 1 — Rule (i), higher charge. The higher the positive charge on the cation, the more strongly it attracts (polarises) the anion's electron cloud; likewise, the higher the negative charge on the anion, the more polarisable it is. So increasing the charge on EITHER ion increases covalent character. Example: since cationic charge rises Na⁺ < Mg²⁺ < Al³⁺, covalent character rises in the same order — NaCl < MgCl₂ < AlCl₃.
Step 2 — Rule (ii), smaller cation, larger anion. A smaller cation concentrates its charge over a smaller volume (higher charge density), so it polarises the anion more strongly; a larger anion, with its outer electrons held more loosely, is itself more easily polarised. Example: LiCl is more covalent than NaCl (Li⁺ smaller than Na⁺); lithium iodide is more covalent than lithium chloride (I⁻ larger, hence more polarisable, than Cl⁻). …
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