Halogen
Halogen, any member of a family of chemical elements that form salts by direct union with metals. (The word halogen means saltmaker.) There are five such elements, all nonmetalic: fluorine, chlorine, bromine, iodine, and the unstable, radioactive element astatine. Halogens react vigorously, often violently, with metals or with hydrogen to form halides. Metal halides are solid, water-soluble salts, such as sodium chloride (table salt). Hydrogen halides, in water solution, form very strong acids, such as hydrochloric acid.
The halogens are poisonous and corrosive. They are very active chemically and are thus not found free in nature. They usually occur in salts. Salt deposits and seawater are two principal sources.
Halogens and their compounds are widely used in industrial processes, in medicine, and in sanitation. Photographic films, disinfectants, insecticides, drugs, bleaches, paints, synthetic textiles, and plastics are some of the products in which they are used.
The halogens make up Group VII-A of the Periodic Table.