Halogens
. Halogens (Greek hals, “salt”; genes, “born”), in chemistry, group of five closely related chemically active elements— fluorine , chlorine , bromine , iodine , and astatine . The name halogen, or salt former, refers to the property of each of the halogens to form with sodium a salt similar to common salt (sodium chloride). Each member of the group has a valence of -1 and combines with metals to form halides, as well as with metals and nonmetals to form complex ions.