Lattice energy (UV) is defined as change in internal energy when one mole of a solid is converted into one mole of infinitely separated ions in the gas phase at 0 K.
The Born-Lande expression for lattice energy may be represented as

${\mathrm{U}}_0=\frac{{\mathrm{N}}_0\mathrm{A}\cdot {\mathrm{Z}}^{+}\cdot {\mathrm{Z}}^{-}\cdot {\mathrm{e}}^2}{4{\mathrm{\pi \epsilon }}_0{\mathrm{r}}_0}\left(1-\frac{1}{\mathrm{n}}\right)$

where N₀ = Avogadro constant

A = Madelung’s constant, which depends upon the geometry of the crystal.
Z⁺ and Z^- are charges on positive and negative ions respectively.
e = charge on electron
r₀ = inter ionic distance
n = A constant called Born exponent (often assumed to be equal to 9)
$\sum _0$ = permittivity of vacuum
In the above equation first term deals with attraction between the ions and the second term$\left(\frac{1}{\mathrm{n}}\right)$ is associated with repulsion.
From the above it becomes clear that lattice energy depends upon
(i) The ionic charges
(ii) The distance between the ions
(iii) Crystal structure