A salt is composed of positive and negative ions. When a salt dissolves in water, each positive ion is surrounded by water molecules with their negative oxygen atoms pointing toward it. Each negative ion also is surrounded by other water molecules, with their positive hydrogens oriented toward it. The ions are said to be hydrated, and we shall see in the next chapter that hydration is an important property of ions. Water helps to break up the solid salt crystal by making strong polar interactions with its ions.