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Nitrogen                                                                                                                              

Standard Sate: gas at 298K

Color: colorless

Nitrogen is a Group 15 element. Nitrogen makes up about 78% of the atmosphere by volume but the atmosphere of Mars contains less than 3% nitrogen. The element seemed so inert that Lavoisier named it azote, meaning "without life". However, its compounds are vital components of foods, fertilizers, and explosives. Nitrogen gas is colourless, odourless, and generally inert. As a liquid it is also colourless and odourless

(N), nonmetallic element of Group Va of the periodic table. It is a
colourless, odourless, tasteless gas that is the most plentiful element in
the Earth's atmosphere, and a constituent of all living matter.

A treatment of nitrogen follows. For additional treatment, see
Chemical Elements: Nitrogen group elements.

Daniel Rutherford, a medical student in Edinburgh, is usually credited
with the discovery of nitrogen (1772) because he was first to publish
his findings; but in England the chemists Joseph Priestley and Henry
Cavendish and in Sweden the chemist Carl Wilhelm Scheele also
discovered it about the same time. The French chemist Antoine
Lavoisier first recognized the gas as an element and named it azote
because of its inability to support life (Greek zoe, "life"). The present
name (from "nitre" plus the suffix "-gen," thus "nitre-forming") was
coined in 1790 to indicate the presence of the element in nitre
(ordinary saltpetre, or potassium nitrate, KNO3).

Occurrence, properties, and uses.


Among the elements, nitrogen ranks sixth in cosmic abundance. It
occurs in the Earth's atmosphere to the extent of 78 percent by
volume, or about 75 percent by weight. Free nitrogen also is found in
many meteorites; in gases of volcanoes, mines, and some mineral
springs; in the Sun; and in some stars and nebulae. In combination it is
found in the minerals nitre and Chile saltpetre (sodium nitrate,
NaNO3); in the atmosphere, rain, soil, and guano as ammonia and
ammonium salts; in seawater as ammonium (NH+4), nitrite (NO-2),
and nitrate (NO-3) ions; and in living organisms as complex organic
compounds such as proteins.

Animals obtain the nitrogen of their tissue proteins from vegetable or
other animal proteins of food. Plants synthesize their proteins from
inorganic nitrogen compounds from soil and to some extent from
uncombined nitrogen in the air. A bacterium living in the roots of
leguminous plants, such as peas, beans, clover, alfalfa, and peanuts,
assimilates atmospheric nitrogen. Certain free-living anaerobic
bacteria and blue-green algae also can extract nitrogen from the air.
Other microorganisms in soils convert ammonium salts to nitrates.
Lightning and sunlight cause a limited amount of nitrogen to combine
with atmospheric oxygen, forming several oxides that are conveyed
by rain in the form of nitric and nitrous acids to the soil, where they
are neutralized, becoming nitrates and nitrites. The nitrogen content
of cultivated soil is generally enriched and renewed artificially by
fertilizers containing nitrates and ammonium salts. Excretion and
decay of animals and plants return nitrogen compounds to the soil
and air, and some bacteria in soil decompose nitrogen compounds
and return the element to the air.

Inhaled nitrogen dissolves slightly in the blood and in other body
fluids; under increased pressure, the amount dissolved is greater. The
bends, or decompression sickness, is caused mainly by bubbles of
nitrogen coming out of solution in the bloodstreams of persons such
as divers, aviators, and those who work in deep caissons on whom the
air pressure has been reduced too quickly.

Commercially, nitrogen is prepared almost entirely by the fractional
distillation of liquid air. Nitrogen, which has a lower boiling point
(-195.8 C, or -320.4 F) than oxygen (-183.0 C, or -297.4 F), tends
to evaporate first. On a small scale, pure nitrogen is made from its
compounds, for example, by heating ammonium nitrite, NH4NO2, or
barium azide, Ba(N3)2.

Chemically, nitrogen gas is quite inert, especially at ordinary
temperatures. Owing to its inertness, nitrogen gas is utilized in the
chemical industry as a diluent or as a blanket to exclude oxygen and
moisture. The low temperature (and inertness) of nitrogen in the
liquid state make it suitable for freeze-drying food and as a refrigerant
when transporting perishable commodities. Liquid nitrogen also has
proved useful in cryogenic research.

Natural nitrogen on Earth consists of a mixture of two stable
isotopes, nitrogen-14 (99.63 percent) and nitrogen-15 (0.37
percent). The first artificially induced nuclear transmutation was
reported (1919) by a British physicist, Ernest Rutherford, who
bombarded nitrogen-14 with alpha particles to form oxygen-17 nuclei
and protons. Three other radioactive isotopes are known:
nitrogen-12, nitrogen-13, and nitrogen-16.

Compounds. Most elemental nitrogen is consumed in the
manufacture of nitrogen compounds.

Large quantities of nitrogen are used together with hydrogen to
produce ammonia, NH3, a colourless gas with a pungent, irritating
odour. The chief commercial method of synthesizing ammonia is the
Haber-Bosch process. Ammonia is one of the two principal nitrogen
compounds of commerce; it has numerous uses in the manufacture of
other important nitrogen compounds. A large portion of
commercially synthesized ammonia is converted into nitric acid
(HNO3) and nitrates, which are the salts and esters of nitric acid.
Much ammonia is used in the ammonia-soda process to produce soda
ash, Na2CO3. Ammonia is also utilized in the preparation of
hydrazine, N2H4, a colourless liquid used as a rocket fuel and in many
industrial processes.

Nitric acid is the other main commercial compound of nitrogen. A
colourless, highly corrosive liquid, it is much used in the production of
fertilizers, dyes, drugs, and explosives. Ammonium nitrate (NH4NO3),
a salt of ammonia and nitric acid, is the most common nitrogenous
component of artificial fertilizers.

With oxygen, nitrogen forms several oxides, including nitrous oxide,
or nitrogen(I) oxide, N2O; nitric oxide, or nitrogen(II) oxide, NO; and
nitrogen dioxide, or nitrogen(IV) oxide, NO2. Many of the nitrogen
oxides are extremely volatile; they are prime sources of pollution in
the atmosphere. Nitrous oxide, also known as laughing gas, is
sometimes used as an anesthetic; when inhaled it produces mild
hysteria. Nitric oxide reacts rapidly with oxygen to form nitrogen
dioxide, an intermediate in the manufacture of nitric acid and a
powerful oxidizing agent utilized in chemical processes and rocket
fuels.

Also of some importance are certain nitrides, solids formed by direct
combination of metals with nitrogen, usually at elevated
temperatures. They include hardening agents produced when alloy
steels are heated in an atmosphere of ammonia, a process called
nitriding. Those of boron, titanium, zirconium, and tantalum have
special applications. One allotrophic form of boron nitride (BN), for
example, is nearly as hard as diamond and less easily oxidized and so
is useful as a high-temperature abrasive.

The inorganic cyanides contain the group CN-. Hydrogen cyanide, or
formonitrile, HCN, is a highly volatile and extremely poisonous gas
that is used in fumigation, ore concentration, and various other
industrial processes. Cyanogen, or oxalonitrile, (CN)2, is also used as
a chemical intermediate and a fumigant.

Azides, which may be either inorganic or organic, are compounds that
contain three nitrogen atoms as a group, represented as (-N3). Most
azides are unstable and highly sensitive to shock. Some of them, such
as lead azide [Pb(N3)2], are used in detonators and percussion caps.
The azides, like the halogen compounds, readily react with other
substances by displacement of the so-called azide group and yield
many kinds of compounds.

Nitrogen forms many thousands of organic compounds. Most of the
known varieties may be regarded as derived from ammonia, hydrogen
cyanide, cyanogen, and nitrous or nitric acid. The amines, amino
acids, and amides, for example, are derived from or closely related to
ammonia. Nitroglycerin and nitrocellulose are esters of nitric acid.
Nitro compounds are obtained from the reaction (called nitration)
between nitric acid and an organic compound. Nitrites are derived
from nitrous acid (HNO2). Nitroso compounds are obtained by the
action of nitrous acid on an organic compound. Purines and alkaloids
are heterocyclic compounds in which nitrogen replaces one or more
carbon atoms. atomic number 7 atomic weight 14.0067 melting point
-209.86C (-345.8F) boiling point -195.8C (-320.4F) density (1 atm,
0 C) 1.2506 g/1 usual oxidation states -3, +3, +5 electron config. 2-5
or 1s22s22p3

"nitrogen" Encyclop�dia Britannica Online.

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