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chlorine(klōr`ēn, klôr`–) [Gr.,=green], gaseous chemical element; symbol Cl; at. no. 17; interval in which at. wt. ranges 35.446–35.457; m.p. −100.98°C;; b.p. −34.6°C;; density 3.2 grams per liter at STP; valence −1, +1, +3, +5, +7. Chlorine is a greenish-yellow poisonous gas with a disagreeable, suffocating odor; it is about two and one-half times as dense as air. Only fluorine among the nonmetals is more chemically active. Chlorine belongs to the halogenhalogen
[Gr.,=salt-bearing], any of the chemically active elements found in Group 17 of the periodic table; the name applies especially to fluorine (symbol F), chlorine (Cl), bromine (Br), and iodine (I).
..... Click the link for more information. family of elements, found in Group 17 of the periodic tableperiodic table,
chart of the elements arranged according to the periodic law discovered by Dmitri I. Mendeleev and revised by Henry G. J. Moseley. In the periodic table the elements are arranged in columns and rows according to increasing atomic number (see the table entitled
..... Click the link for more information. . The gas is composed of diatomic molecules (Cl2) with molecular weight 70.906. Chlorine was discovered in 1774 by K. W. ScheeleScheele, Karl Wilhelm
, 1742–86, Swedish chemist, b. Stralsund. He is known as the discoverer of many chemical substances. He was a pharmacist in Stockholm, in Uppsala (1770–75), and then in Köping. He prepared and studied oxygen c.
..... Click the link for more information. , who thought it was a compound of oxygen; it was named and identified as an element by Sir Humphry DavyDavy, Sir Humphry,
1778–1829, English chemist and physicist. The son of a woodcarver, he received his early education at Truro and was apprenticed (1795) to a surgeon-apothecary at Penzance.
..... Click the link for more information. in 1810.
Chlorine is soluble in water; its aqueous solution, called chlorine water, consists of a mixture of chlorine, hydrochloric acid, and hypochlorous acid; only a part of the chlorine introduced actually goes into solution, the major part reacting chemically with the water. Chlorine water has strong oxidizing properties resulting from the oxygen set free when the unstable hypochlorous acid decomposes. Chlorine reacts readily with hydrogen to form hydrogen chloride. It burns if ignited in a hydrogen atmosphere and, if unignited, can form explosive mixtures with hydrogen; it also unites with the hydrogen in compounds such as turpentine, a hydrocarbon. In the presence of moisture it combines directly with certain metals, such as copper and iron, to form chlorideschloride
, chemical compound containing chlorine. Most chlorides are salts that are formed either by direct union of chlorine with a metal or by reaction of hydrochloric acid (a water solution of hydrogen chloride) with a metal, a metal oxide, or an inorganic base.
..... Click the link for more information. . Iron ignites when heated in a chlorine atmosphere. With metals and oxygen, chlorine forms several chlorateschlorate
, salts of chloric acid, HClO3, and perchloric acid, HClO4, respectively. Chloric Acid and Its Salts
Chloric acid, HClO3·7H2
..... Click the link for more information. ; it also combines with many nonmetals and certain radicals.
Because of its activity chlorine does not occur uncombined in nature, but its compounds are numerous and abundant. Sodium chloride (common salt) is present in seawater, salt wells, and large salt deposits, often in association with other chlorides. Chlorine is produced commercially chiefly by the electrolysis of sodium chloride, either molten or in solution. Other chlorides are sometimes employed. Chlorine can also be prepared from hydrochloric acid by oxidation of the hydrogen chloride (Deacon's process) and from bleaching powder.
Chlorine is used in water purification; as a disinfectantdisinfectant,
agent that destroys disease-causing microorganisms and their spores. Disinfectants, or germicides, are sometimes considered to be s