BOILING POINT : −34°C
DENSITY : 3.214 g/cm 3 (liq. at 0°C)
MOST COMMON IONS : Cl 1− , Cl 1+ , Cl 3+ , Cl 5+ , Cl 7+
Chlorine is one of the halogen family of elements and the first of that family to be discovered. Swedish chemist Carl Wilhelm Scheele produced chlorine in 1774 by the reaction of manganese dioxide (MnO 2 ) with a solution of hydrochloric acid (HCl). In 1810 English chemist Sir Humphry Davy determined chlorine to be an element and named it for the color of the gas (the Greek word chloros means "pale green").
Elemental chlorine is a diatomic molecule and is toxic. It has a high electronegativity that is about equal to that of oxygen. The most common oxidation numbers are 7, 5, 3, 1, and −1.
Chlorine is the most abundant of the halogens having a concentration of 19.87 parts per thousand (ppt) by weight in seawater and an average of 0.17 ppt in Earth's crust. It is produced commercially by electrolysis of seawater and brines. Sodium chloride (NaCl), or common table salt, can be obtained from seaside evaporation pools or mined from underground deposits.
Chlorine and its compounds have a large number of everyday uses. Chlorine is used in water purification as well in the production of safe plumbing components constructed of polyvinyl chloride (PVC). Chlorinated dyes, medicines, pesticides, disinfectants, and solvents have widespread applications. Chlorofluorocarbon compounds (CFCs) were once widely used as refrigerants, solvents, foaming agents, and spray-can propellants, but are now banned by international agreement due to the role of those compounds in the depletion of Earth's protective ozone layer. Chlorine was used during World War I (1914–1918) as a chemical warfare agent.
Lide, David R., ed. (2003). The CRC Handbook of Chemistry and Physics , 84th edition. Boca Raton, FL: CRC Press.
Winter, Mark. "Chlorine." The University of Sheffield and WebElements Ltd., UK. Available from http://www.webelements.com .