group, grouping - any number of entities (members) considered as a unit

astatine, At, atomic number 85 - a highly unstable radioactive element (the heaviest of the halogen series); a decay product of uranium and thorium

atomic number 35, Br, bromine - a nonmetallic largely pentavalent heavy volatile corrosive dark brown liquid element belonging to the halogens; found in sea water

atomic number 17, chlorine, Cl - a common nonmetallic element belonging to the halogens; best known as a heavy yellow irritating toxic gas; used to purify water and as a bleaching agent and disinfectant; occurs naturally only as a salt (as in sea water)

atomic number 9, fluorine, F - a nonmetallic univalent element belonging to the halogens; usually a yellow irritating toxic flammable gas; a powerful oxidizing agent; recovered from fluorite or cryolite or fluorapatite

atomic number 53, I, iodin, iodine - a nonmetallic element belonging to the halogens; used especially in medicine and photography and in dyes; occurs naturally only in combination in small quantities (as in sea water or rocks)