The type of inorganic solid formed between elements in group 1 alkali metals and group 7 halogens of the periodic table is an ionic solid. These compounds are formed through the transfer of electrons from the alkali metal to the halogen, resulting in the formation of positive and negative ions that are held together by strong electrostatic forces in a crystal lattice structure. Examples of such compounds include sodium chloride NaCl , potassium bromide KBr , and lithium iodide LiI .