Physical Chemistry/Lattice Enthalpy

Lattice enthalpy is the enthalpy change when one mole of an ionic compound is formed from its gaseous ions under standard conditions.

M+ (g) + X- (g) > MX (s)

It is a measure of how strong the ionic lattice is within the compound. Lattice energies are exothermic. The more negative the value, the stronger the bonding.