The elements of group 17 (formerly called group VIIa in North America and VIIb in Europe) include the gases fluorine and chlorine, and the nonmetals bromine, iodine and astatine. These highly reactive elements, excepting astatine, are collectively known as the halogens. The name derives from Greek hal, salt, and gen, forming or producing. Although never found in nature as free elements, the saltsóchlorides, bromides, iodides and other halogen compoundsóhave been in use since antiquity. The highly water-soluble salts are important constituents of seawater. The atoms of the elements in group 15 have 7 valence electrons.