Halogen, HAL uh juhn. The halogens are the chemical elements astatine (chemical symbol, At), fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). They are nonmetals, and make up part of the seventh main group in the periodic system of the elements. Halogen means salt producer. Many of the salts in the sea are compounds of halogens with metals. Common table salt, the best known such compound, is sodium chloride.