Nitrogen is a chemical element; it has symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh in total abundance in the Milky Way and the Solar System. At standard temperature and pressure, two atoms of the element bond to form N2, a colourless and odourless diatomic gas. N2 forms about 78% of Earth's atmosphere, making it the most abundant chemical species in air. Because of the volatility of nitrogen compounds, nitrogen is relatively rare in the solid parts of the Earth.
It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772 and independently by Carl Wilhelm Scheele and Henry Cavendish at about the same time. The name was suggested by French chemist Jean-Antoine-Claude Chaptal in 1790 when it was found that nitrogen was present in nitric acid and nitrates. Antoine Lavoisier suggested instead the name azote, from the "no life", as it is an asphyxiant gas; this name is used in a number of languages, and appears in the English names of some nitrogen compounds such as hydrazine, azides and azo compounds.
Elemental nitrogen is usually produced from air by pressure swing adsorption technology. About 2/3 of commercially produced elemental nitrogen is used as an inert (oxygen-free) gas for commercial uses such as food packaging, and much of the rest is used as liquid nitrogen in cryogenic applications. 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), the second strongest bond in any diatomic molecule after carbon monoxide (CO),Common Bond Energies (D) and Bond Lengths (r) . wiredchemist.com dominates nitrogen chemistry. This causes difficulty for both organisms and industry in converting N2 into useful compounds, but at the same time it means that burning, exploding, or decomposing nitrogen compounds to form nitrogen gas releases large amounts of often useful energy. Synthetically produced ammonia and nitrates are key industrial fertilisers, and fertiliser nitrates are key pollutants in the eutrophication of water systems. Apart from its use in fertilisers and energy stores, nitrogen is a constituent of organic compounds as diverse as aramids used in high-strength fabric and cyanoacrylate used in superglue.
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% nitrogen by mass, the fourth most abundant element in the body after oxygen, carbon, and hydrogen. The nitrogen cycle describes the movement of the element from the air, into the biosphere and organic compounds, then back into the atmosphere. Nitrogen is a constituent of 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 metabolising into nitric oxide. Many notable nitrogen-containing drugs, such as the natural caffeine and morphine or the synthetic amphetamines, act on receptors of animal neurotransmitters.
History
Nitrogen compounds have a very long history, ammonium chloride having been known to Herodotus. They were well known by the Middle Ages. Alchemists knew nitric acid as aqua fortis (strong water), as well as other nitrogen compounds such as ammonium salts and nitrate salts. 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 discovery of nitrogen is attributed to the Scottish physician Daniel Rutherford in 1772, who called it noxious air.Rutherford, Daniel (1772) "Dissertatio Inauguralis de aere fixo, aut mephitico " (Inaugural dissertation on the air [called] fixed or mephitic), M.D. dissertation, University of Edinburgh, Scotland. English translation: Though he did not recognise it as an entirely different chemical substance, he clearly distinguished it from Joseph Black's "fixed air", or carbon dioxide. The fact that there was a component of air that does not support combustion was clear to Rutherford, although he was not aware that it was an element. Nitrogen was also studied at about the same time by Carl Wilhelm Scheele,Carl Wilhelm Scheele, Chemische Abhandlung von der Luft und dem Feuer [Chemical treatise on air and fire] (Upsala, Sweden: Magnus Swederus, 1777; and Leipzig, (Germany): Siegfried Lebrecht Crusius, 1777). In the section titled "Die Luft muß aus elastischen Flüßigkeiten von zweyerley Art, zusammengesetzet seyn." (The air must be composed of elastic fluids of two sorts), pp. 6–14, Scheele presents the results of eight experiments in which air was reacted with various substances. He concluded (p. 13): "So viel sehe ich aus angeführten Versuchen, daß die Luft aus 2 von einander unterschiedenen Flußigkeiten bestehe, von welchen die eine die Eigenschaft das Phlogiston anzuziehen gar nicht äussere, die andere aber zur solchen Attraction eigentlich aufgeleget ist und welche zwischen dem 3:ten und 4:ten Theil von der ganzen Luftmasse aus machet." (So I see [this] much from the experiments [that were] conducted: that the air consists of two fluids [that] differ from one another, of which the one doesn't express at all the property of attracting phlogiston; the other, however, is capable of such attraction and which makes up between 1/3 and 1/4 part of the entire mass of the air.) Henry Cavendish, ; see p. 225. and Joseph Priestley, ; see: "VII. Of air infected with the fumes of burning charcoal." pp. 225–28. who referred to it as burnt air or phlogisticated air. French chemist Antoine Lavoisier referred to nitrogen gas as "mephitic air" or azote, from the Greek word (azotikos), "no life", because it is asphyxiant.Lavoisier, Antoine with Robert Kerr, trans., Elements of Chemistry, 4th ed. (Edinburgh, Scotland: William Creech, 1799), pp. 85–86. [p. 85]: "In reflecting upon the circumstances of this experiment, we readily perceive; that the mercury, during its calcination [i.e., roasting in air], absorbs the salubrious and respirable part of the air, or, to speak more strictly, the base of this respirable part; that the remaining air is a species of mephitis [i.e., a poisonous gas emitted from the earth], incapable of supporting combustion or respiration; ... " [p. 86]: "I shall afterwards shew, that at least in our climate, the atmospheric air is composed of respirable and mephitic airs, in the proportion of 27 and 73; ... "Lavoisier, Antoine with Robert Kerr, trans., Elements of Chemistry, 4th ed. (Edinburgh, Scotland: William Creech, 1799), p. 101: "The chemical properties of the noxious portion of the atmospheric air being hitherto but little known, we have been satisfied to derive the name of its base from its known quality of killing such animals as are forced to breathe it, giving it the name of azot, from the Greek privitive particle α and ξωη, vita; hence the name of the noxious part of atmospheric air is azotic gas." In an atmosphere of pure nitrogen, animals died and flames were extinguished. Though Lavoisier's name was not accepted in English since it was pointed out that all gases but oxygen are either asphyxiant or outright toxic, it is used in many languages (French, Italian, Portuguese, Polish, Russian, Albanian, Turkish, etc.; the German Stickstoff and Dutch stikstof similarly refer to the same characteristic, viz. ersticken/stikken meaning "to choke or suffocate") and still remains in English in the common names of many nitrogen compounds, such as hydrazine and compounds of the azide ion. Finally, it led to the name "pnictogens" for the group headed by nitrogen, from the Greek πνίγειν "to choke".Greenwood and Earnshaw, pp. 406–07
The English word nitrogen (1794) entered the language from the French , coined in 1790 by French chemist Jean-Antoine Chaptal (1756–1832),Chaptal, J. A. and Nicholson, William trans. (1800) Elements of Chemistry, 3rd ed. London, England: C.C. and J. Robinson, vol. 1. pp. xxxv–xxxvi: "In order to correct the Nomenclature on this head [i.e., in this regard], nothing more is necessary than to substitute to [i.e., for] this word a denomination which is derived from the general system made use of; and I have presumed to propose that of Nitrogene Gas. In the first place, it is deduced from the characteristic and exclusive property of this gas, which forms the radical of the nitric acid. By this means we shall preserve to the combinations [i.e., compounds] of this substance the received [i.e., prevailing] denominations, such as those of the Nitric Acid, Nitrates, Nitrites, &c." from the French nitre (potassium nitrate, also called saltpetre) and the French suffix -gène, "producing", from the Greek -γενής (-genes, "begotten"). Chaptal's meaning was that nitrogen is the essential part of nitric acid, which in turn was produced from nitre. In earlier times, nitre had been confused with Egyptian "natron" (sodium carbonate) – called νίτρον (nitron) in Greek – which, despite the name, contained no nitrate.nitrogen . Etymonline.com. Retrieved 2011-10-26.
The earliest military, industrial, and agricultural applications of nitrogen compounds used saltpetre (sodium nitrate or potassium nitrate), most notably in gunpowder, and later as fertiliser. In 1910, Lord Rayleigh discovered that an electrical discharge in nitrogen gas produced "active nitrogen", a monatomic allotrope of nitrogen.Strutt, R. J. (1911) "Bakerian Lecture. A chemically active modification of nitrogen, produced by the electric discharge", Proceedings of the Royal Society A, 85 (577): 219–29. The "whirling cloud of brilliant yellow light" produced by his apparatus reacted with mercury to produce explosive mercury nitride.. 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 now relies on synthetic nitrogen fertilisers. 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.
Properties
Atomic
A nitrogen atom has seven electrons. In the ground state, they are arranged in the electron configuration 1s2s2p2p2p. It, therefore, has five valence electrons in the 2s and 2p orbitals, three of which (the p-electrons) are unpaired. It has one of the highest electronegativities among the elements (3.04 on the Pauling scale), exceeded only by chlorine (3.16), oxygen (3.44), and fluorine (3.98). (The light noble gases, helium, neon, and argon, would presumably also be more electronegative, and in fact are on the Allen scale.) Following periodic trends, its single-bond covalent radius of 71 pm is smaller than those of boron (84 pm) and carbon (76 pm), while it is larger than those of oxygen (66 pm) and fluorine (57 pm). The nitride anion, N3−, is much larger at 146 pm, similar to that of the oxide (O2−: 140 pm) and fluoride (F−: 133 pm) anions. The first three ionisation energies of nitrogen are 1.402, 2.856, and 4.577 MJ·mol−1, and the sum of the fourth and fifth is . Due to these very high figures, nitrogen has no simple cationic chemistry.Greenwood and Earnshaw, p. 550