* Nitrogen is a member of the main group nonmetals family:
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NITROGEN / N / 7
Elemental nitrogen occurs as N2, a colorless, odorless, inert gas.
Two isotopes occur in nature:
N<14/7> / 99.6%
N<15/7> / 0.4%.
Both are stable.
atomic weight: 14.0067
abundance: 30th
density of N2: 1.2506 gm/l
melting point: -210 C
boiling point: -196 C
valence: <3> 5
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The "NO2-" group is known as "nitrite", while the "NO3" group is known as "nitrate" and the "NH4+" group is known as "ammonium".
The atmosphere consists of about 78% diatomic nitrogen gas, N2. Most industrial nitrogen is obtained by liquefying air and then warming it: since nitrogen has a lower boiling point than oxygen (-196 C versus -183 C), the N2 boils off first. Such "fractional distillation" is used to produce tens of millions of tonnes of nitrogen a year.
Nitrogen is a major constituent of biomolecules. Ammonia (NH3) and nitric acid (HNO3) are widely used in the chemical industry. Since soil fertility is strongly based on nitrogen, ammonium nitrate (NH4NO3) is widely used as a fertilizer. A mix of ammonium nitrate and fuel oil (ANFO) is often used as an explosive for mining and earth-moving. High explosives are often based on nitrogen-based compounds, for example nitroglycerine and TNT. The unstable nitrogen-based compound hydrazine (N2H4) is used as a rocket fuel, particularly for small thrusters, since it will "burn" (or more precisely decompose) without oxygen if run over a catalyst. It is, however, toxic and corrosive.
Liquid nitrogen is used as a cryogenic coolant, and nitrous oxide (N2O) is used as a medical anesthesia of sorts in the form of "laughing gas". However, other oxides of nitrogen, such as nitrogen monoxide (NO) and nitrogen dioxide (NO2) are toxic. Such "NOx" compounds are major constituents of air pollutants from automobile exhausts. Nitrogen gas is also used as a filler gas in aircraft fuel tanks since it is inert, helping suppress fire and explosion.
