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Nitrogen is a chemical element with symbol N and atomic number 7. It is the lightest pnictogen and at room temperature, it is a transparent, odorless diatomic gas. Nitrogen is a common element in the universe, estimated at about seventh in total abundance in the Milky Way and the Solar System. On Earth, the element forms about 78% of Earth's atmosphere and as such is the most abundant uncombined element. The element nitrogen was discovered as a separable component of air, by Scottish physician Daniel Rutherford, in 1772. Many industrially important compounds, such as ammonia, nitric acid, organic nitrates (propellants and explosives), and cyanides, contain nitrogen. The extremely strong triple bond in elemental nitrogen (N≡N) dominates nitrogen chemistry, causing difficulty for both organisms and industry in converting the N2 into useful compounds, but at the same time causing release of large amounts of often useful energy when the compounds burn, explode, or decay back into nitrogen gas. Synthetically-produced ammonia and nitrates are key industrial fertilizers and fertilizer nitrates are key pollutants in causing the eutrophication of water systems. Outside the major uses of nitrogen compounds as fertilizers and energy-stores, nitrogen is a constituent of organic compounds as diverse as Kevlar fabric and cyanoacrylate "super" glue. Nitrogen is a constituent of molecules in every major pharmacological drug class, including antibiotics. Many drugs are mimics or prodrugs of natural nitrogen-containing signal molecules: for example, the organic nitrates nitroglycerin and nitroprusside control blood pressure by being metabolized to nitric oxide. Plant alkaloids (often defense chemicals) contain nitrogen by definition, and thus many notable nitrogen-containing drugs, such as caffeine and morphine are either alkaloids or synthetic mimics that act (as many plant alkaloids do) on receptors of animal neurotransmitters (for example, synthetic amphetamines). Nitrogen occurs in all organisms, primarily in amino acids (and thus proteins), in the nucleic acids (DNA and RNA) and in the energy transfer molecule adenosine triphosphate. The human body contains about 3% by mass of nitrogen, the fourth most abundant element in the body after oxygen, carbon, and hydrogen. The nitrogen cycle describes movement of the element from the air, into the biosphere and organic compounds, then back into the atmosphere. ==History and etymology== Nitrogen is formally considered to have been discovered by Scottish physician Daniel Rutherford in 1772, who called it ''noxious air''. Though he did not recognize it as an entirely different chemical substance, he clearly distinguished it from Joseph Black's "fixed air", or carbon dioxide.〔Aaron J. Ihde, The Development of Modern Chemistry, New York 1964.〕 The fact that there was a component of air that does not support combustion was clear to Rutherford. Nitrogen was also studied at about the same time by Carl Wilhelm Scheele, Henry Cavendish, and Joseph Priestley, who referred to it as ''burnt air'' or ''phlogisticated air''. Nitrogen gas was inert enough that Antoine Lavoisier referred to it as "mephitic air" or ''azote'', from the Greek word ''azotos'', "lifeless".〔''Elements of Chemistry'', trans. Robert Kerr (Edinburgh, 1790; New York: Dover, 1965), 52.〕 In it, animals died and flames were extinguished. This "mephitic air" consisted mostly of N2, but might also have included more than 1% argon. Lavoisier's name for nitrogen is used in many languages (French, Italian, Polish, Russian, Albanian, Turkish, etc.) and still remains in English in the common names of many compounds, such as hydrazine and compounds of the azide ion. The English word nitrogen (1794) entered the language from the French ''nitrogène'', coined in 1790 by French chemist Jean-Antoine Chaptal (1756–1832), from the Greek νίτρον ''nitron'', "sodium carbonate" and the French ''-gène'', "producing" from Greek -γενής ''-genes'', "producer, begetter". The gas had been found in nitric acid. Chaptal's meaning was that nitrogen gas is the essential part of nitric acid, in turn formed from saltpeter (potassium nitrate), then known as niter.〔(nitrogen ). Etymonline.com. Retrieved 2011-10-26.〕 Nitrogen compounds were well known by the Middle Ages. Alchemists knew nitric acid as ''aqua fortis'' (strong water). The mixture of nitric and hydrochloric acids was known as ''aqua regia'' (royal water), celebrated for its ability to dissolve gold (the ''king'' of metals). The earliest military, industrial, and agricultural applications of nitrogen compounds used saltpeter (sodium nitrate or potassium nitrate), most notably in gunpowder, and later as fertilizer. In 1910, Lord Rayleigh discovered that an electrical discharge in nitrogen gas produced "active nitrogen", a monatomic allotrope of nitrogen. The "whirling cloud of brilliant yellow light" produced by his apparatus reacted with quicksilver to produce explosive mercury nitride.〔(Lord Rayleigh's Active Nitrogen ). Lateralscience.co.uk. Retrieved 2011-10-26.〕 For a long time sources of nitrogen compounds were limited. Natural sources originated either from biology or deposits of nitrates produced by atmospheric reactions. Nitrogen fixation by industrial processes like the Frank–Caro process (1895–1899) and Haber–Bosch process (1908–1913) eased this shortage of nitrogen compounds, to the extent that half of global food production (see applications) now relies on synthetic nitrogen fertilizers. At the same time, use of the Ostwald process (1902) to produce nitrates from industrial nitrogen fixation allowed the large-scale industrial production of nitrates as feedstock in the manufacture of explosives in the World Wars of the 20th century. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「nitrogen」の詳細全文を読む スポンサード リンク
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