The dissolving of BeO is an example of the usefulness of acids and bases in promoting reactions that do not proceed easily or at all in neutral water solution.

Because BeO is insoluble in pure water but reacts with either an acid (like a base would) or a base (like an acid would), we say that it is amphoteric, from a Greek word meaning "both behaviors."

BeO is on the borderline between bases and acids, and the explanation for its amphoteric behavior is to be found in the greater electronegativity of Be than Li, and the partial covalent character of the Be-O bond.

Other, heavier metals, such as aluminum, which also are on the borderline between metallic and nonmetallic behavior, have amphoteric oxides, with both basic and acidic properties.