Topic: halogen

halogen [Gr.,=salt-bearing], any of the chemically active elements found in Group 17 of the periodic table ; the name applies especially to fluorine (symbol F), chlorine (Cl), bromine (Br), and iodine (I). Astatine (At), formerly known as alabamine, is a radioactive element also classed as a halogen; its most stable isotope (which does not occur in nature) has a half-life of less than 8 1/2 hr. The chemical and physical properties of astatine are not well known; it is believed to resemble iodine. The halogens are the best-defined family of chemical elements. Chemica... Read more