Which of the following is least ionic?
- CoCl2
- KCl
- BaCl2
- AgCl
Answer
(4) AgCl
Solution
Fajans' rule: covalent character ∝ polarising power of the cation
Ag+ ( [Kr]4d10, 18-electron shell): d-electrons shield the nucleus poorly ⇒ very high polarising power ⇒ AgCl most covalent
K+, Ba2+: large, noble-gas configuration ⇒ highly ionic
Co2+ (3d7): small, but no 18-electron shell ⇒ intermediate
∴ Ionic character: AgCl < CoCl2 < BaCl2 < KCl
Answer: (4)