Final answer:
The magnitude of the lattice energy of a salt is primarily determined by the charge and size of the ions. Greater ionic charges and smaller ionic sizes lead to higher lattice energies, which contribute significantly to the stability of ionic compounds.
Step-by-step explanation:
The factors responsible for the magnitude of the lattice energy of a salt include the charge on an ion and its size. The lattice energy of an ionic crystal increases rapidly as the charges of the ions increase and the sizes of the ions decrease. For example, the lattice energy of LiF, with ions carrying a charge of +1 and -1, is 1023 kJ/mol. In comparison, the lattice energy of MgO, with ions carrying a charge of +2 and -2, is 3900 kJ/mol, quadrupling due to the doubling of the charge on both the cation and anion while the internuclear distances are nearly the same.
Lattice energy is usually the most important energy factor in determining the stability of an ionic compound. It depends largely on the Coulombic attraction between ions, which is influenced by their charge and distance apart, essentially their size. However, other factors such as covalent character and electron-electron interactions also play a role, particularly in complex ionic solids with various lattice structures.