[Ajathashatru]

First of all, sorry if this sounds silly.

I understand Lattice energy as the energy required for the gaseous ions to come together and form an ionic solid. If so, higher lattice energy would mean a higher ionic character of the bond.

But if we take an example of LiCl and NaCl, LiCl has higher lattice energy despite Fajan's rule stating that the smaller cation (with higher charge density) shall polarize the anion's electron cloud, and impart covalent character to the bond. If it is so, shouldn't LiCl have more covalent character than NaCl? Then how come LiCl has larger Lattice Energy? Isn't Lattice energy and Covalent Character directly related?

[Orcio_87]

Then how come LiCl has larger Lattice Energy?

Lattice energy increases with Madelung parameter (related to crystal structure), charge of both cation and anion and crystal compressibility, while drops with distance between cation and anion.

Distance between Li-Cl is about 10 % smaller than Na-Cl.

Isn't Lattice energy and Covalent Character directly related?

How do you then explain very high lattice energy in covalent solids like diamond ?