bromine: a nonmetallic heavy volatile corrosive dark brown liquid element belonging to the halogens; found in sea water
chemical element: any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter
ion exchange: a process in which ions are exchanged between a solution and an insoluble (usually resinous) solid; widely used in industrial processing