Polarisation

1. Polarisation and Polarisability

2. Polarisation and Polarisability
Polarisation- The negative cloud of electrons is
distorted due to influence of a positive atomic nuclei.
Polarisability- ability of atom/ion to be distorted due
to influence of electric field such that of an atom.

3. + -
Ideal ion pair with no polarisation
- - - - - - - - Dashed lines represent hypothetical unpolarized ions

4. +
-
Mutually Polarised ion Pair

5. +
-
Polarisation sufficient to form a covalent bond

6. Fajans Rules
• High charge and small size cation exert greater polarisation in
anions than lower charged cations.
(Li + 76 pm) (Mg2+ 72 pm)
• High charge and large size anion experience greater polarisation by
the cations. (I- 206 pm) (Se2- 198 pm) (As3- 222 pm)
• Electronic configuration with partially filled d electron will be more
polarising than ions having noble gas configuration.
Kazimierz Fajans