Nitrogen is a chemical element, typically found as a gas in its elemental form. It has the chemical symbol N, atomic number (number of protons) Z = 7, and a standard atomic weight of 14.0067 g/mol.
Nitrogen has two stable isotopes: 14N, with a natural abundance of 99.632%, and 15N, with a natural abundance of 0.368%. Other isotopes of nitrogen are unstable, decaying in a few minutes or fractions of a second. 14N has an atomic mass of 14.0030740052 u, and 15N has an atomic mass of 15.0001088984 u.
Nitrogen has three unpaired electrons in its outermost shell and therefore can form three single covalent bonds with three other atoms, sharing one electron with each, as in NH3, ammonia; a single covalent bond with one atom and one double covalent bond with another, as in azo dyes, -N=N-; and, one triple covalent bond, as in N2. No other element has more oxidation states than nitrogen, which can have oxidation states of -3, -2, -1, 0, +1, +2, +3, +4, and +5.
Covalently bonded with itself in a triple bond (sharing six electrons in total), the diatomic gaseous nitrogen molecule, (N2), makes up about 78% by volume (75% by mass) of dry air. At the Earth's surface normal temperature and pressure N2 exists as a gas with no taste, color or odor. The nitrogen molecule is chemically rather inert, it does not burn, does not support combustion and is only slightly soluble in water. At high temperature it combines with oxygen to form NOx, a generic designation for the mono-nitrogen oxides NO and NO2 (nitric oxide and nitrogen dioxide) which are formed during many combustion processes.
Liquid nitrogen, which boils at -195.8 C, is used as a cryogenic liquid to preserve organic material such as bacterial strains or sperm samples. It is also used, usually with liquid helium, to cool superconducting magnetic materials for a variety of instruments including mass spectrometers and nuclear magnetic resonance spectrometers.
Nitrogen is important for living organisms because it is an important element of amino acids, nucleic acids (DNA & RNA) and many other nitrogenous organic compounds. Synthetic fertilizers contain nitrogen obtained from air by the Haber-Bosch process, a so-called nitrogen fixation process.
Ammonia and ammonium salts
Ammonia production on an industrial-scale uses the Haber-Bosch process, in which nitrogen and hydrogen gasses react, in the presence of iron, heat and pressure, to produce ammonia. Ammonia can also be produced by reacting ammonium salts with excess alkali, as shown in the following equation:
NH4+ + OH- → NH3 + H2O
Ammonia has a very pungent odor. Because the molecule has a pyramidal structure, it is very polar and can form hydrogen bonds with water so that saturated aqueous ammonia is 15 M.