A highly irritating, greenish-yellow halogen element, existing as a diatomic gas, Cl₂, and capable of combining with nearly all other elements, produced principally by electrolysis of sodium chloride and used widely to disinfect water, as a bleaching agent, and in the manufacture of many important compounds including chlorates, sodium hypochlorite, and chloroform. Atomic number 17; atomic weight 35.453; freezing point -100.5°C; boiling point -34.04°C; specific gravity 1.56 (-33.6°C); valence 1, 3, 5, 7. See Periodic Table.