Chlorine is a greenish-yellow gas that can be readily liquefied at 5170 Tarr or 6.8 atmospheres at 20°C (68°F) and has a very disagreeable odor. Its element symbol is Cl, atomic number is 17, and atomic mass is 35.453.
Chlorine’s melting point is -101°C or 149.8°F. The boiling point is -34.05°C or -29.29°F at one atmosphere pressure. Chlorine is a member of the halogen group.
Chlorine was discovered by Swedish scientist Karl Wilhelm in 1784, but he initially thought it was a compound rather than an element. In 1810, Sir Humphrey Davy named it Chlorine, from the Greek word meaning greenish-yellow”. Chlorine is used in bleaching agents, disinfectants, monomers (plastics), solvents, and pesticides. It is also used for bleaching paper pulp and other organic materials, preparing bromine (a poisonous element that is dark reddish-brown at room temperature), tetraethyl lead, and killing germs in water, particularly in swimming pools and hot tubs. Like every member of the halogen group, chlorine has a tendency to gain one electron and become a chloride ion. Chlorine strongly reacts with metals to form mostly water-soluble chlorides.
Chlorine also strongly reacts with nonmetals such as sulfur, phosphorus, and other halogens. If hydrogen and chlorine gases are mixed and kept in a cool dark place, the mixture would be stable. However, if exposed to sunlight, it would cause a strong explosion. If a burning candle is placed in a sealed container of chlorine, it would keep burning and produce thick black smoke, leaving behind soot. Chlorine can form five oxides: chlorine monoxide, dichloride monoxide, chlorine dioxide, chlorine heptoxide, and chlorine hexoxide. Chlorine is used in bleaching agents, disinfectants, monomers (plastics), solvents, and pesticides.
Chlorine is used for bleaching paper pulp and other organic materials, preparing bromine (a poisonous element that is dark reddish-brown at room temperature), tetraethyl lead, and killing germs in water, particularly in swimming pools and hot tubs. Chlorine is made by electrolysis of a salt solution, with a by-product of sodium hydroxide. Some industrial chlorine is made by oxidizing hydrogen chloride (a colorless, corrosive, nonflammable gas with a penetrating, suffocating odor). Chlorine was the first substance used as a poisonous gas in World War I, along with gases like tear gas, phosgene (a lung irritant), and mustard gas. Flame-throwers were also tried, but at first were thought ineffective because of their short range. However, when napalm (made up of palmitic and napthenic acids), a sort of thick, sticky gasoline, was developed, flame throwers were quite useful in World War II.
Bibliography: Microsoft Encarta. Copyright 1994 Microsoft Corporation. Asimov, Isaac, Building Blocks of the Universe, rev. ed.
References: Downs, A. J., The Chemistry of Chlorine, Bromine, Iodine and Astatine (1975); Hamilton, E. I., The Chemical Elements and Man (1978); Nechamkin, Howard, Chemistry of the Elements (1968); Ruben, Samuel, Handbook of the Elements, 2nd ed. (1974).
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