NITROGEN, N (from the Latin word "Nitrogenium" * EN: nitrogen; DE: Stickstoff; FR: azote, nitrogene; ES: nitrogeno; RU: азот) is the chemical element of the V group of the Periodic System by Mendeleev, the atomic number is 7, the atomic weight is 14.0067. It has been discovered in 1772 by the English researcher Daniel Rutherford.

Under normal conditions, nitrogen is the gas without the colour or odour. The natural nitrogen comprises the two stable isotopes: 14N (99.635%) and 15N (0.365%). The molecule of the nitrogen is diatomic, the atoms are linked by the covalent triple bond NN. The diameter of the nitrogen molecule, which has been determined in many ways, is 3.15-3.53 angstroms. The molecule of nitrogen is very stable, the energy of the dissociation is 942.9 kilojoules per mol. The constants of the molecular nitrogen are: the temperature of the melting is minus 209.86 degrees Celsius, the temperature of the boiling is minus 195.8 degrees Celsius, the density of the gaseous nitrogen is 1.25 kilograms per cubic metre, the density of the liquid nitrogen is 808 kilograms per cubic metre.

Nitrogen exists in the two solid state versions: the cubic alpha-form with the density of 1026.5 kilograms per cubic metre, and the hexagonal beta-form with the density of 879.2 kilograms per cubic metre. The heat of the melting is 25.5 kilojoules per kilogram, the heat of the evaporation is 200 kilojoules per kilogram. The surface tension of the liquid nitrogen in the contact with air is 8.5 * 10^-3 newtons per metre; the permittivity is 1.000538. The solubility of the nitrogen in the water (cubic centimetres per 100 millilitres of H2O) is: 2.33 (at 0 degrees Celsius), 1.42 (at 25 degrees Celsius), and 1.32 (at 60 degrees Celsius). The outer electron shell of the atom of nitrogen comprises 5 electrons. The oxidation states of nitrogen change from 5 (in N2O5) to 3 (in NH3).

Nitrogen may react under the normal conditions with the compounds of the transition metals (Ti, V, Mo, etc.), forming the complexes or reducing itself with the formation of the ammonia and hydrazine. Nitrogen reacts with such active metals as lithium, calcium, magnesium during the heating to the relatively low temperatures. Nitrogen reacts with most other elements at the high temperature and in the presence of the catalysts. The compounds of nitrogen with oxygen (N2O, NO, N2O5) are well studied. Nitrogen combines with hydrogen only at high temperatures and in the presence of the catalysts; then the ammonia NH3 is formed. Nitrogen does not react with the halogens directly; thus they get all nitrogen halides only by the indirect way, for example they get the nitrogen fluoride NF3 during the reaction of the fluorine with ammonia. There does not proceed the direct combination of nitrogen with sulfur either. The cyanogen (CN)2 is formed during the interaction of the hot coke with nitrogen. The active nitrogen, being the mixture of the nitrogen atoms and molecules, which have the elevated reserve of the energy, may form during the action of the electrical discharges on the common nitrogen. The active nitrogen reacts very energetically with the oxygen, hydrogen, vapours of the sulfur, phosphorus, and certain metals.

Nitrogen is one of the most abundant elements on the Earth, and most of its mass (approximately 4 * 10^15 tonnes) is concentrated in the free state in the atmosphere. 2 * 10^6 tonnes of nitrogen are released into the atmosphere every year during the volcanic activity. The non-significant amount of nitrogen is concentrated in the lithosphere (the average content in the lithosphere is 1.9 * 10^-3 %). The natural compounds of nitrogen are the ammonium chloride and (saltpetre) various nitrates. The nitrides of nitrogen may be formed only at high temperatures and pressures, which were likely to exist at the earliest stages of the development of the Earth. The large accumulations of the saltpetre are found only in the conditions of the dry desert climate (Chile, India, Egypt, Spain, etc.). The small amounts of the fixed nitrogen are located in the coal (1-2.5%) and oil (0.02-1.5%), as well as in the waters of the rivers, seas and oceans. Nitrogen is accumulated in the soils (0.1%) and living organisms (0.3%). Nitrogen is the constituent of the protein molecules and numerous natural organic compounds.

There proceeds in the nature the cycle of the nitrogen, which comprises the cycle of the molecular atmospheric nitrogen in the biosphere; the cycle of the chemically bound nitrogen in the atmosphere; the cycle in the lithosphere of the surface nitrogen, which was buried together with the organic substance, with the return of it back into the atmosphere. In the past times, they mined nitrogen for the industry entirely from the deposits of the natural saltpetre, the quantity of which in the world is very limited. Especially large depositions of nitrogen in the form of the sodium nitrate are located in Chile; the extraction of the saltpetre in the certain years amounted to more than 3 million tonnes.

They produce nitrogen mainly by the separation of the liquefied in advance air, which is then subjected to distillation. The major share of the produced nitrogen is used for the production of the ammonia, which is then processed into the nitric acid, fertilizers, and explosives. Free nitrogen is used in many industries as the inert medium during the various chemical and metallurgical processes. Liquid nitrogen is used in various refrigeration systems. The works are performed on the usage of the liquid nitrogen for the freezing of the unstable rocks (mainly clayish) during the sinking of the mine shafts, as the safe source of the energy for the mining machines, and also for the fighting with the mining fires, where the usage of the nitrogen allows to sharply decrease the content of oxygen in the seat of the fire. They effectively displace the oil by pumping nitrogen into the oil reservoirs after the water flooding during the development of the oil fields. Nitrogen is also used for the maintenance of the pressure in the wells during drilling.