Lattice Energies of Ionic Crystals

Lattice energy is the energy released when one mole of oppositely charged gaseous ions forms an ionic crystal. It measures the strength of the ionic attraction holding the crystal together.

This attraction between ions follows Coulomb’s law and depends on the ionic charges and the distance between ions. Larger charges strengthen the attraction, while a greater separation weakens it.

In a lattice, each ion interacts with many neighboring ions. It experiences attractions from opposite charges and repulsions from like charges.

To account for all lattice interactions, the Madelung constant, M, is introduced. Including M into Coulomb’s expression and multiplying by Avogadro’s number gives the molar lattice energy.

At short distances, electron clouds overlap and cause repulsion. Born described this repulsion using a constant and a distance term raised to the Born exponent, n.

Combining these attractive and repulsive energies gives the Born–Landé equation for the lattice energy.

The Born–Mayer equation later refined this model using a repulsive range parameter, ρ. It describes the distance at which repulsive forces remain significant to the overall lattice energy.