Chlorine, symbol Cl, is a greenish-yellow gaseous element. In the group 17 of the periodic table, chlorine is one of the halogens. The atomic number of chlorine is 17. Elementary chlorine was first isolated in 1774 by the Swedish chemist Carl Wilhelm Scheele, who thought that gas was a compound of oxygen. It was not until 1810 that the British chemist Sir Humphry Davy proved that chlorine was an element and gave it its present name.

At ordinary temperatures, chlorine is a greenish-yellow gas that can readily be liquefied under pressure of 6.8 atmospheres, at 20 degrees Celsius (68 degrees pharenhit). The gas has an irritating odor and can sometimes be dangerous. Chlorine does not occur in nature, but its compounds are common minerals, and it is the 20th most abundant element in the earth's crust. Cl has a specific gravity o

Most chlorine is produced by the electrolysis of ordinary salt solution, with sodium hydroxide as a by-product. Because the demand for chlorine exceeds that for sodium hydroxide, some industrial chlorine is produced by treating salt with nitrogen oxides or by oxidizing hydrogen chloride. Chlorine is shipped liquid in steel bottles or tank cars. It is used for bleaching paper pulp and other organic materials, destroying germ life in water, and preparing bromine, tetraethyl lead, and other important products.

They are also used in household construction. It can be found in PVC window frames; plumbing pipes; concrete; fiberglass insulation; paint; nylon carpeting; and garden sprinklers. It can also be found in household appliances such as; toiletries; cosmetics; televisions; compact discs; and fabric and garment cleaners.

Chlorine is also an important factor in making pharmaceuticals such as product to prevent AIDS, allergies, arthritis, cancer, depression, diabetes, heart disease, hypertension, infections, pneumor and ulcers.

Chlorine is used in water purification, as a disinfectant and as an antiseptic. Chlorinated hydrocarbons have been used extensively as pesticides. Some examples are dieldrin, aldrin, endrin, lindane, chlordane, and heptachlor. These compounds resist degradation and have become very troublesome environmental pollutants. Carbon tetrachloride and trichloroethylene are used as solvents. The Freon refrigerants are hydrocarbons that have been reacted with chlorine and fluorine. Chlorine is an important constituent of many poison gases. It is used in such compounds as calo

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