-- -- -- C N O Si P S Element Fact In 1961, the International Union of Pure and Applied Chemistry adopted the isotope carbon-12 as the basis of atomic weight, which has a mass of exactly 12.000 atomic mass unit.

Nitrogen, N Atomic number: 7 Atomic mass: 14.0067(2) Natural abundance: 19 ppm Isotopes: 14N (14.003074) - 99.63% 15N (15.000109) - 0.37% History and Production Derived from Latin nitrum or Greek nitron meaning native soda and genes, forming. However, A. L. Lavoisier called azote, meaning no life, due to the asphyxiating properties of the gas. Until this day, some nitrogen compounds still bear this name in the form of azo, diazo, azide, etc. The gas was discovered by D. Rutherford in 1772, but isolated independently by C.W. Scheele and H. Cavendish. It can be directly obtained by liquefaction and distillation of Earth atmosphere. Nitrogen also evolves when ammonium nitrite solution is heated. Nitrogen coumpounds are used in foods, fertilizer, explosives and poisons. When heated with hydrogen, ammonia is formed (Haber cycle). Ammonia is prepared in large amount in industry for fertilizer, production of nitric acid and in the electronic industry as a blanketing medium. Liquid nitrogen is used in missile work and in oil industry to build pressure in order to force crude oil upwards. Physical Data It is a colorless, odorless gas and is generally inert. Liquid nitrogen has similar appearance to water, which is also colorless and odorless. It is the most abundant element accessible, which exists as diatomic form in atmosphere. However, it only presents in comparatively much smaller amount in crustal rocks and exists mainly in saltpetre, KNO3 and Chile saltpetre, NaNO3. Nitrogen is an important constituent in biological molecules which consists of about 15% by weight of proteins. There is a continuous interchange of nitrogen between the atmosphere and biosphere which is called the nitrogen cycle. Interatomic distance: 109.8 pm Melting point: -210.0°C Boiling point: -198.79°C Thermal conductivity/Wm-1K-1: 0.02598 (27°C) Density/kgm-3: 1.2506 (0°C), 880 (b.p.) Standard Thermodynamic Data (atomic gas) Enthalpy of formation: 472.7 kJ/mol Gibbs free energy of formation: 455.5 kJ/mol Entropy: 153.2 J/mol K Heat capacity: 20.8 J/mol K Electronic data Electronic configuration: [He] 2s2 2p3 Term symbol: 4S3/2 Electron affinity: (not stable) kJ/mol   Electronegativity (Pauline): 3.04 Ionization energy (first, second, third): 1402.33, 2856.09, 4578.16 kJ/mol Chemical Properties The gaseous, diatomic nitrogen is chemically inert due to its strong triple bond and the lack of polarity. However, at higher temperatures, it combines with metals (such as Be, Al etc) to give nitrides.

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