Nitrogen is a 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
|Name, Symbol, Number
||Nitrogen, N, 7
|Group, Period, Block
||15 (VA), 2 , p
||1.2506 kg/m3(273K), NA
|Atomic radius (calc.)
||65 (56) pm
|van der Waals radius
|e- 's per energy level
|Oxidation states (Oxide)
||±3,5,4,2 (strong acid)
|State of matter
||63.14 K (-345.75 °F)
||77.35 K (-320.17 °F)
||13.54 ×10-6 m3/mol
|Heat of vaporization
|Heat of fusion
||ND Pa at __ K
|Speed of sound
||334 m/s at 298.15 K
||3.04 (Pauling scale)
|Specific heat capacity
||ND 106/m ohm
|1st ionization potential
|2nd ionization potential
|3rd ionization potential
|4th ionization potential
|5th ionization potential
|6th ionization potential
|7th ionization potential
|SI units & STP
are used except where noted.
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% of the Earth's atmosphere. It condenses
at 77 K and freezes at 63 K. Liquid nitrogen is a common cryogen.
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. Nitrogen is used as a coolant both for the immersion
freezing of food products and for transportation of foods, for the
preservation of bodies and reproductive cells (sperm and egg), and
for the stable storage of biological samples in biology.
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.
Nitrogen in its liquid state (often referred to as LN2)
is often used in cryogenics. Liquid nitrogen is produced by distillation
from liquid air. At atmospheric pressure, nitrogen condenses at
-195.8 degrees Celsius. (-320.4 degrees Fahrenheit). It is the liquid
coolant frequently used for demonstrations in science education.
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 the largest single component of the Earth's atmosphere
(78.1% by volume, 75.5% by weight) and is acquired for industrial
purposes by the fractional distillation of liquid air. 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
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
The main hydride of nitrogen is ammonia (NH3) although
hydrazine (N2H4) is also well known. Ammonia
is somewhat more basic than water, and in solution forms ammonium
ions (NH4+). Liquid ammonia in fact slightly
amphiprotic and forms ammonium and amide ions (NH2-);
both amides and nitride (N3-) salts are known, but decompose
in water. Singly and doubly substituted compounds of ammonia are
called amines. Larger chains, rings and structures of nitogen hydrides
are also known but virtually unstable.
Other classes of nitrogen anions are azides (N3-),
which are linear and isoelectronic to carbon dioxide. Another molecule
of the same structure is dinitrogen monoxide (N2O), or
laughing gas. This is one of a variety of oxides, the most prominent
of which are nitrogen monoxide (NO) and nitrogen dioxide (NO2),
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 (N2O3)
and dinitrogen pentoxide (N2O5), are actually
fairly unstable and explosive. The corresponding acids are nitrous
(HNO2) and nitric acid (HNO3), with the corresponding
salts called nitrites and nitrates. Nitric acid is one of the few
acids stronger than hydronium.
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.
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.
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.