chlorine (Cl) /klôr″ēn/ , a yellowish-green gaseous element of the halogen group. Its atomic number is 17; its atomic weight mass is 35.453. It has a strong, distinctive odor; is irritating to the respiratory tract; and is poisonous if ingested or inhaled. It occurs in nature chiefly as a component of sodium chloride in seawater and in salt deposits. It is used as a bleach and as a disinfectant to purify water for drinking or for use in swimming pools. Chlorine compounds in general use include many solvents, cleaning fluids, and chloroform. Most of the solvents and cleaning fluids containing chlorine are toxic when inhaled or ingested.
