Arrange the following in increasing order of their covalent character.
A. CaF₂
B. CaCl₂
C. CaBr₂
D. CaI₂
Choose the correct answer from the options given below.

Solution

Chemistry ma’am · 3 steps

Same cation every time, so the anion decides: the bigger the halide, the easier it is to distort.

1. Fajans' rules. An ionic bond picks up covalent character when the cation pulls the anion's electron cloud towards itself. This is called polarisation. The larger and softer the anion, the more it gets polarised, and the more covalent the bond.
2. Fix the cation. All four compounds have the same cation, Ca²⁺, so its polarising power is the same in each. Only the size of the halide ion changes, and size grows down the group: F⁻ < Cl⁻ < Br⁻ < I⁻.

   Compound	Anion	Anion size	Covalent character
   A. CaF₂	F⁻	smallest	least
   B. CaCl₂	Cl⁻	larger	more
   C. CaBr₂	Br⁻	larger still	more still
   D. CaI₂	I⁻	largest	most

3. So. Covalent character increases as A < B < C < D, which is option (b).

The idea to keep. When the cation is the same, compare only the anions: a bigger anion has a looser electron cloud, gets polarised more, and so gives the bond more covalent character.

Answer from the NTA final answer key. Solution by PrepWiser.