Ionic bonds exist between metals and non metals for example sodium and chlorine. Metals have one to three electrons in their outer shell which can be transferred to a non metal. This means that the metal now has a full outer shell, as does the non metal because it has gained electrons in its outer shell. The transfer of electrons forms one positive and one negative ions which are held together by strong electrostatic forces of attraction. Therefore an ionic compound is composed of many oppositely charged ions arranged as positive-negative-positive, to minimise repulsion of like charges, and this results in a giant lattice structure.