Place the following compounds in order of increasing magnitude of lattice energy

Question

Ga₂O₃   RbI  MgS   K₂S   

Answer 1

Lattice energy is determined by the charge on the atoms making up the lattice and by the atomic radii of those atoms.

Ga has a 3+ and O has a 2 -. These will attract strongly giving it a high lattice energy (q1q2 = 6)

Rb has 1+ and I a 1- so not such a strong attraction and not a high LE (q1q2 = 1)

Mg has 2+ and S a 2- so stronger than RbI but not as strong as Ga₂O₃ LE (q1q2 = 4)

K has 1+ and S a 2- (q1q2 = 2) So in order of increasing LE we have... RbI < K₂S < MgS < Ga₂O₃