Lattice Energy
The energy released when one mole of an ionic solid is formed from its constituent gaseous ions.
Formula / equation
U ∝ (z⁺z⁻) / (r⁺ + r⁻)
Unit
kJ/mol
In depth
Lattice energy rises steeply with ionic charge and falls as ionic radii increase, so doubly charged small ions give the most tightly bound lattices. It cannot be measured directly and is instead obtained from a Born–Haber cycle. It largely determines melting point, hardness and solubility.
Examples in the real world
MgO releases 3795 kJ/mol against NaCl's 787 kJ/mol, which is why MgO melts above 2800 °C.