An ionic substance is a substance made up of cations and anions arranged in a regular, repeating geometric pattern throughout a crystal. The strong electrostatic attractions between the oppositely charged ions give these substances high melting points and make them conduct electricity when molten or dissolved. Sodium chloride (NaCl) is a typical ionic substance, in contrast to a molecular substance held together by weaker forces.

离子化合物是由阳离子和阴离子在整个晶体中按规则重复的几何方式排列而成的物质。带相反电荷离子之间强烈的静电吸引使这类物质具有高熔点,并在熔融或溶解时能导电。氯化钠(NaCl)是典型的离子化合物;与之相对的是靠较弱作用力结合的分子物质。