Nitrogen is the
chemical element in the
periodic table that has the symbol
N and
atomic number 7. A common normally colorless, odorless, tasteless and mostly
inert diatomic non-metal gas, nitrogen constitutes 78 percent of
Earth's atmosphere and is a constituent of all living tissues. Nitrogen forms many important compounds such as
ammonia,
nitric acid, and
cyanides.
Notable characteristics
Nitrogen is a non-metal, with an
electronegativity of 3.0. It has five electrons in its outer shell, so is trivalent in most compounds. Pure nitrogen is an unreactive colorless
diatomic gas at room temperature, and comprises about 78.08% of the
Earth's atmosphere. It
condenses at 77 K and freezes at 63 K. Liquid nitrogen is a common cryogen.
Applications
The greatest single commercial use of nitrogen is as a component in the manufacture of
ammonia via the
Haber process. Ammonia is subsequently used for
fertilizer production and to produce
nitric acid. Nitrogen is used as an inert atmosphere in tanks of explosive liquids, during production of
electronic parts such as
transistors,
diodes, and
integrated circuits, and is used in the manufacture of
stainless steel.
Liquid nitrogen (often referred to as LN
2) is used as a coolant for the immersion freezing and transportation of
food products, for the
preservation of bodies and reproductive cells (
sperm and
egg), and for the stable storage of
biological samples. It is also used in the study of
cryogenics, and for demonstrations in
science education. Liquid nitrogen is produced by
distillation from
liquid air.
The salts of
nitric acid include some important compounds, for example potassium nitrate, or saltpeter, and
ammonium nitrate. The former compound is a component of
gunpowder, the latter important in
fertilizer. Nitrated organic compounds, such as
nitroglycerin and
trinitrotoluene, are often explosives.
Nitric acid is used as an oxidizer in liquid fueled
rockets.
Hydrazine and hydrazine derivatives find use as rocket
fuels.
Liquid nitrogen can also be used in the treatment of
warts and of
actinic keratosis (skin lesions that may progress to forms of
skin cancer if untreated).
History
Nitrogen (
Latin nitrum,
Greek Nitron meaning "native soda", "genes", "forming") is formally considered to have been discovered by
Daniel Rutherford in 1772, who called it
noxious air or
phlogisticated air. That there was a fraction of air that did not support
combustion was well known to the late 18th century
chemist. Nitrogen was also studied at about the same time by
Carl Wilhelm Scheele,
Henry Cavendish, and
Joseph Priestley, who referred to it as
burnt air or
dephlogisticated air. Nitrogen gas was inert enough that
Antoine Lavoisier referred to it as
azote, which stands for
without life.
Compounds of nitrogen were known in the
Middle Ages. The
alchemists knew
nitric acid as
aqua fortis. The mixture of nitric and
hydrochloric acids was known as
aqua regia, celebrated for its ability to dissolve
gold.
Nitrogen is also used in filling automotive tires due to its relatively flat line of thermal expansion.
Occurrence
Nitrogen is the largest single component of the Earth's
atmosphere (78.084% by volume, 75.5% by weight) and is acquired for industrial purposes by the fractional
distillation of liquid air or by mechanical means of gaseous air (i.e. pressurised reverse osmosis membrane or PSA (Pressure Swing Adsorption).
Compounds that contain this element have been observed in outer space. Nitrogen-14 is created as part of the
fusion processes in
stars. Nitrogen is a large component of animal waste (for example,
guano), usually in the form of
urea,
uric acid, and compounds of these nitrogenous products.
Molecular nitrogen has been known to occur in
Titan's atmosphere for some time, and has now been detected in interstellar space by David Knauth and coworkers using the
Far Ultraviolet Spectroscopic Explorer.
Compounds
The main
hydride of nitrogen is
ammonia (N
H3) although
hydrazine (N
2H
4) is also well known. Ammonia is somewhat more basic than
water, and in solution forms
ammonium ions (NH
4+). Liquid ammonia is in fact slightly amphiprotic and forms ammonium and
amide ions (NH
2-); both amides and
nitride (N
3-) salts are known, but decompose in water. Singly and doubly substituted compounds of ammonia are called
amines. Larger chains, rings and structures of nitrogen hydrides are also known but virtually unstable.
Other classes of nitrogen
anions are
azides (N
3-), which are linear and
isoelectronic to
carbon dioxide. Another
molecule of the same structure is
dinitrogen monoxide (N
2O), or laughing gas. This is one of a variety of oxides, the most prominent of which are nitrogen monoxide (NO) and
nitrogen dioxide (NO
2), which both contain an unpaired
electron. The latter shows some tendency to
dimerize and is an important component of smog.
The more standard oxides,
dinitrogen trioxide (N
2O
3) and
dinitrogen pentoxide (N
2O
5), are actually fairly unstable and explosive. The corresponding acids are
nitrous (HNO
2) and
nitric acid (HNO
3), with the corresponding salts called
nitrites and
nitrates. Nitric acid is one of the few acids stronger than
hydronium.
Biological role
Nitrogen is an essential part of
amino and
nucleic acids which makes nitrogen vital to all life.
Legumes like the
soybean plant, can recover nitrogen directly from the atmosphere because their roots have nodules harboring microbes that do the actual conversion to
ammonia in a process known as
nitrogen fixation. The legume subsequently converts ammonia to nitrogen oxides and amino acids to form
proteins.
Isotopes
There are two stable
isotopes: N-14 and N-15. By far the most common is N-14 (99.634%), which is produced in the
CNO cycle in stars. The rest is N-15. Of the ten isotopes produced synthetically, one has a
half life of nine minutes and the remaining isotopes have half lives on the order of seconds or less.
Biologically-mediated reactions (e.g., assimilation, nitrification, and denitrification) strongly control nitrogen dynamics in the soil. These reactions almost always result in N-15 enrichment of the substrate and depletion of the product. Although precipitation often contains subequal quantities of
ammonium and nitrate, because ammonium is preferentially retained by the canopy relative to atmospheric nitrate, most of the atmospheric nitrogen that reaches the soil surface is in the form of nitrate. Soil nitrate is preferentially assimilated by tree roots relative to soil ammonium.
Precautions
Nitrate fertilizer washoff is a major source of ground water and river
pollution. Cyano (-
CN) containing compounds form extremely poisonous salts and are deadly to many animals and all
mammals.
See also
References
External links
Category:Nonmetals
Category:Pnictogens
Category:Nitrogen metabolism
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