Any of five nonmetallic element s
fluorine , chlorine , bromine , iodine , and astatine
with similar chemical properties.
They occur in the second rightmost column of the periodic table as usually arranged. All are highly reactive oxidizing agents (see oxidation-reduction ) with valence 1 (for fluorine, the only valence). They combine readily with most metals and nonmetals to form a variety of compounds and never occur uncombined in nature. A radioactive element, astatine occurs naturally in minute amounts as an intermediate decay product; it has no stable nonradioactive salt s formed with metal atoms (halides) are very stable; sodium chloride is the most familiar. The halogen lamp takes its name from the halogens included in the gas within its tungsten-filament bulb, added to prolong filament life and increase brightness.