Fajan's rule

Fajan's Rule for determining polarisibility of molecules

1. Shri shankaracharya mahavidyalaya junwani , bhilai Presented by Dr. Neelam Department of chemistry Fajan’s Rule

2. Fajan’s Rule POLARISATION : ( Fajan’s Rule) (Covalent nature in ionic bond) Polarisation Power : The ability of cation to polarise a nearby anion is called Polarisation power of cation . Polarisation ∝ Covalent character

3. Fajan’s rule : (Factors Affecting Polarisation) Size of cation : - Polarisation of the anion increases as the size of cation decreases. Greatest polarising power of Be 2+ , shows its maximum covalent character In a period.

4. (b) Size of anion : - If the size of the anion increases for a given cation , the covalent character increases/Nature Polarisation ∝ size of anion. (c) Charge on cation and anion : - Polarisation ∝ charge on cation anion Charge on cation ∝ Polarisation (covalent character) - Charge on cation increases - Covalent character increases Ionic character decreases (M.P. decreases) Charge on anion ∝ polarisation ∝ covalent nature ∝

5. (d) Electronic configuration of cation : - Polarisation capacity of cation having pseudo inert gas configuration is high. If the size of cations is same than that of cation having inert gas configuration. Cu + and Na + both the cation (Pseudo & inert) have same charge and size but polarising power of Cu + is more than Na + because- So CuCl has more covalent character than NaCl .

6. Covalent character ∝ Boiling point 1 Covalent character ∝ 1 Covalent character ∝ Solubility 1 Covalent character ∝ Ionic character 1 Covalent character ∝ ∝ Size of anion ∝ charge of cation Size of cation 1 Covalent character ∝ Size of anion ∝ polarising power Melting point

7. Covalent character ∝ Size of anion = F - < O 2- < N 3- Ionic character ∝ Size of cation = Be 2+ < Mg 2+ < Ca 2+ < Sr 2+ < Ba 2+ Size of cation = Al 3+ < Na + < Sn 4+ < Pb 2+ Size of cation = C 4+ < B 3+ < Be 2+ < Li +

8. 9 Thank you