Lattice energy is the energy required to break apart an ionic solid and transform its constituent atoms into gaseous ions. It is the energy released when gaseous ions bind to form an ionic solid. Lattice energy is a form of potential energy used to explain the stability of ionic solids.
The lattice energy of a crystalline solid is typically defined as the energy of formation of the crystal from infinitely-separated atoms, ions and molecules. The crystalline structure allows each ion to interact with many other oppositely charged ions, which leads to a highly favorable change in the amount of heat content used or released in the system. The strength of the bond between the ions of opposite charge in an ionic compound is determined by the charges on the ions and the distance between the centers of the ions when they combine to form a crystal. The interaction between oppositely charged ions releases a lot of energy, which results in high melting and boiling points in ionic solids.
Estimation of the strength of the bonds in an ionic compound can be done by measuring the compound’s lattice energy. The lattice energy of NaCl, for instance, is the energy given off when Na+ and Cl- ions in the gas phase combine to form the lattice of alternating Na+ and Cl- ions in the NaCl crystal.