It is a white crystalline solid. It is very toxic. It can be made by reacting chlorine with mercury. It is not ionic, like most metal-nonmetal chemical compounds are. For example, it evaporates easily when heated, while ionic compounds like sodium chloride stay solid. It dissolves in water, but much better in hot water than in cold water. It also dissolves in chloride solutions. It is very corrosive and a strong oxidizing agent. It reacts with bases to make mercury(II) oxide.