Question

What is lattice energy and what role does it play in the stability of ionic compounds?

Short answer

Lattice energy is the energy required to convert one mole of an ionic solid into its individual ions in gaseous states, and it plays a critical role in the stability of ionic compounds. The higher the lattice energy, the more stable the ionic compound. It depends on the charge and radii of the ions, with higher charges and smaller radii resulting in stronger interactions and thus, higher lattice energy.

Step-by-step solution

Define Lattice Energy

Lattice energy can be defined as the energy required to convert one mole of an ionic solid into its constituent ions in gaseous states. It is an exothermic process, meaning it releases energy, and is usually reported in kilojoules per mole (kJ/mol). In mathematical form, this can be represented as: M\(^{+}\)X\(^{-}\)(s) --> M\(^{+}\)(g) + X\(^{-}\)(g) where M\(^{+}\) and X\(^{-}\) represent the cations and anions in the ionic compound.

Role of Lattice Energy in Stability of Ionic Compounds

The lattice energy plays a key role in the stability of ionic compounds. The higher the lattice energy, the stronger are the forces of attraction between the ions, and thus, requiring more energy to separate them. Therefore, ionic compounds with higher lattice energy are more stable. Conversely, those with lower lattice energy are less stable. The stability and hence the lattice energy, depends on the charges of the ions and the radii of the ions in the compound. The lattice energy increases with increasing charge and decreasing ionic radii.

Example of Lattice Energy

For instance, consider Sodium Chloride (NaCl), when Na and Cl combine to form the NaCl compound and lattice, there is a release of energy due to the formation of ionic bonds. This energy (lattice energy) contributes towards the stability of NaCl. The factors that influenced this stability are the charges of the Na and Cl ions, and their radii. The released lattice energy makes the NaCl compound more stable.