Question

arrange the following compounds in terms in increasing lattice energy and explain
NaF, Fe2o3, MgO, Cal2

Answer 1

The lattice energy U is proportional to the product of the charge of the ions.

U α q₁q₂ where q₁ and q₂ are the charges on the cation and the anion.

Compute the product for the given compounds:

Compound	Charge on cation	Charge on anion	│q1q2│
NaF	+1	-1	1
Fe2O3	+3	-2	6
MgO	+2	-2	4
CaI2	+2	-1	2

The radii of the ions are more or less comparable, expect for CaI₂ where the anion is much smaller than the cation. Hence, there will not be close packing of the ions and therefore, the lattice will be less stable than the lattices of the other three compounds. Hence, CaF₂ will have the lowest lattice energy.

For the other three compounds, the lattice energy will be directly proportional to q₁q₂. Hence, the increasing order of lattice energy is

CaI₂ < NaF < MgO < Fe₂O₃ (lattice energy increases).