Burning beryllium metal in dry air produces beryllium oxide, BeO. This is a salt with and ions in a crystal lattice, although the attractions between and have an appreciable covalent character. Since each Be atom can give up two electrons, and each oxygen atom needs two electrons, the atoms combine in a 1:1 ratio.

There is an important difference between BeO and Because beryllium is more electronegative than lithium, the Be-O bond is not entirely ionic, but has a considerable electron-sharing character. The electrons that surround an ion to complete its neon shell actually are shared to a degree with the beryllium atoms.

BeO is not a completely covalent solid like diamond, but it does have a partial covalent character that makes it more difficult to pull apart than .