chlorine gas
carl wilhelm scheele
['nikola tesla', 'conway', 'annibale de gasparis', 'harry edwin wood', 'ingrid', 'bickley', 'gause', 'henry bessemer', 'ernest rutherford', 'christopher cockerell', 'nanking', 'roger penrose', 'james watt', 'robert luther', 'tycho', 'gustav rose', 'edward said', 'karl reinmuth', 'takashi murakami', 'nicolas bourriaud', 'heinrich schenker', 'lionel penrose', 'carl auer von welsbach', 'charles darwin', 'lewis swift', 'birmingham university', 'michael brown', 'herschel', 'alessandro malaspina', 'egide walschaerts', 'sir arthur evans', 'nikolai stepanovich chernykh', 'sylvain arend', 'icao', 'sir nigel gresley', 'james bradley', 'edwin mcmillan', 'hermann goldschmidt', 'franz kaiser', 'cavendish', 'marguerite laugier', 'sir alexander fleming', 'carolyn shoemaker', 'stallman', 'tsutomu seki', 'marija gimbutas', 'isaac newton', 'george westinghouse', 'william rowan hamilton', 'ptolemy', 'alexander grothendieck', 'frederick scott archer', 'blackberry', 'cyril jackson', 'charles messier', 'vint cerf', 'august derleth', 'george maciunas', 'paolo maffei', 'leibniz', 'ole kirk christiansen', 'claude chappe', 'henri lebesgue', 'ephraim shay', 'alonzo church', 'chad trujillo', 'august kopff', 'lyudmila chernykh', 'bernhard schmidt', 'bartolomeo cristofori', 'otto hahn', 'malcolm mackerras', 'silas weir mitchell', 'julian huxley', 'lord rayleigh', 'babbage', 'carl friedrich gauss', 'gotthold ephraim lessing', 'harold urey', 'maurice martenot', 'franz anton mesmer', 'johan gadolin', 'werner heisenberg', 'max wolf', 'linear', 'noam chomsky', 'auguste charlois', 'arnold schoenberg', 'toshimasa furuta', 'karl drais', 'edwin hubble', 'urata', 'vapnik', 'moog', 'thomas newcomen', 'indiana asteroid program', 'christopher latham sholes', 'ernest johnson', 'hendrik van gent']
Chlorine
Chlorine is a chemical element with symbol Cl and atomic number 17. It has a relative atomic mass of about 35.5. Chlorine is in the halogen group (17) and is the second lightest halogen, following fluorine. The element is a yellow-green gas under standard conditions, where it forms diatomic molecules. Chlorine has the highest electron affinity and the third highest electronegativity of all the reactive elements. For this reason, chlorine is a strong oxidizing agent. Free chlorine is rare on Earth, and is usually a result of direct or indirect oxidation by oxygen. The most common compound of chlorine, sodium chloride (common salt), has been known since ancient times. Around 1630, chlorine gas was first synthesized in a chemical reaction, but not recognized as a fundamentally important substance. Characterization[clarification needed] of chlorine gas was made in 1774 by Carl Wilhelm Scheele, who supposed it to be an oxide of a new element. In 1809, chemists suggested that the gas might be a pure element, and this was confirmed by Sir Humphry Davy in 1810, who named it from Ancient Greek: χλωρός (khlôros) "pale green". Nearly all chlorine in the Earth's crust occurs as chloride in various ionic compounds, including table salt. It is the second most abundant halogen and 21st most abundant chemical element in Earth's crust. Elemental chlorine is commercially produced from brine by electrolysis. The high oxidizing potential of elemental chlorine led commercially to free chlorine's bleaching and disinfectant uses, as well as its many uses as an essential reagent in the chemical industry. Chlorine is used in the manufacture of a wide range of consumer products, about two-thirds of them organic chemicals such as polyvinyl chloride, as well as many intermediates for production of plastics and other end products which do not contain the element. As a common disinfectant, elemental chlorine and chlorine-generating compounds are used more directly in swimming pools to keep them clean and sanitary. In the form of chloride ions, chlorine is necessary to all known species of life. Other types of chlorine compounds are rare in living organisms, and artificially produced chlorinated organics range from inert to toxic. In the upper atmosphere, chlorine-containing organic molecules such as chlorofluorocarbons have been implicated in ozone depletion. Small quantities of elemental chlorine are generated by oxidation of chloride to hypochlorite in neutrophils, as part of the immune response against bacteria. Elemental chlorine at high concentrations is extremely dangerous and poisonous for all living organisms, and was used in World War I as the first gaseous chemical warfare agent.