Nitrogen
Nitrogen is a
chemical element which has the symbol
N and
atomic number 7 in the
periodic table. Elemental nitrogen is a colorless, odorless, tasteless and mostly
inert diatomic gas at
standard conditions, constituting 78.08% percent of
Earth's atmosphere. Nitrogen is a constituent element of all living
tissues and
amino acids. Many industrially important compounds, such as
ammonia,
nitric acid, and
cyanides, contain nitrogen.
Nitrogen is a
non-metal, with an
electronegativity of 3.0. It has five
electrons in its outer shell and is therefore
trivalent in most compounds. Nitrogen
condenses at 77°
K at
atmospheric pressure and freezes at 63° K. Liquid nitrogen is a common
cryogen.
Nitrogen is the largest single component of the Earth's
atmosphere (78.084% by volume, 75.5% by weight).
14Nitrogen is created as part of the
fusion processes in
stars.
Compounds that contain this element have been observed by astronomers, and molecular nitrogen has been detected in
interstellar space by
David Knauth and coworkers using the
Far Ultraviolet Spectroscopic Explorer. Molecular nitrogen is a major constituent of
Titan's thick atmosphere, and occurs in trace amounts of other planetary atmospheres.
Nitrogen is present in all living tissues as proteins, nucleic acids and other molecules. It is a large component of animal waste (for example,
guano), usually in the form of
urea,
uric acid, and compounds of these nitrogenous products.
See also Nitrate minerals, Ammonium minerals.There are two stable
isotopes of nitrogen:
14N and
15N. By far the most common is
14N (99.634%), which is produced in the
CNO cycle in
stars and the remaining is
15N. Of the ten isotopes produced synthetically,
13N 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
15N 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.The molecular nitrogen in Earth's atmosphere is 0.73% comprised of the isotopomer
14N
15N and almost all the rest is
14N
2.
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
fixed 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
phlogisticated air. Nitrogen gas was
inert enough that
Antoine Lavoisier referred to it as
azote, from the
Greek word αζωτος meaning "lifeless". Animals died in it, and it was the principal component of air in which animals had suffocated and flames had burned to extinction. This term has become the
French word for "nitrogen" and later spread out to many other languages.
Compounds of nitrogen were known in the
Middle Ages. The
alchemists knew
nitric acid as
aqua fortis (strong water). The mixture of nitric and
hydrochloric acids was known as
aqua regia (royal water), celebrated for its ability to dissolve
gold (the
king of metals). The earliest industrial and
agricultural applications of nitrogen compounds used it in the form of
saltpeter (
sodium- or
potassium nitrate), notably in
gunpowder, and much later, as
fertilizer, and later still, as a chemical
feedstock.
See also
nitrogen cycleNitrogen is an essential part of
amino acids and
nucleic acids both of which are essential to all life. Specific bacteria (e.g. Rhizobium
trifolium) possess
nitrogenase enzymes which can fix atmospheric nitrogen (see
nitrogen fixation) into a form (ammonium ion) which is chemically useful to higher organisms. This process requires a large amount of energy and anoxic conditions. Such bacteria may be free in the soil (e.g. azotobacter) but normally exist in a symbiotic relationship in the root nodules of leguminous plants (e.g. clover or the soya bean plant). Nitrogen fixating bacteria can be symbiotic with a number of unrelated plant species. Common examples are legumes, alders, lichens, casuarina, myrica, liverwort, and gunnera.
As part of the symbiotic relationship, the plant subsequently converts the ammonium ion to nitrogen oxides and amino acids to form
proteins and other biologically useful molecules, such as
alkaloids. In return, the plant secretes sugars to the symbiotic bacteria.
Some plants are able to assimilate nitrogen directly in the form of nitrates which may be present in soil from natural mineral deposits, artificial fertilizers, animal waste, or organic decay (as the product of bacteria, but not bacteria specifically associated with the plant). Nitrates absorbed in this fashion are converted to nitrites by the enzyme
nitrate reductase, and then converted to ammonia by another enzyme called
nitrite reductase.
Nitrogen compounds are basic building blocks in animal biology. Animals use nitrogen-containing
amino acids from plant sources, as starting materials for all nitrogen-compound animal biochemistry, including the manufacture of
proteins and
nucleic acids. Many saltwater fish manufacture large amounts of
trimethylamine oxide to protect them from the high osmotic effects of their environment (conversion of this compound to
dimethylamine is responsible for the early odor in unfresh saltwater fish: PMID 15186102). In animals, the free radical molecule
nitric oxide (NO), which is derived from an amino acid, serves as an important regulatory molecule for circulation.
Animal metabolism of NO results in production of
nitrite. Animal metabolism of nitrogen in proteins generally results in excretion of
urea, while animal metabolism of nucleic acids results in excretion of
urea and
uric acid. The characteristic odor of animal flesh decay is caused by nitrogen-containing long-chain
amines, such as
putrescene and
cadaverine.
Decay of organisms and their waste products may produce small amounts of nitrate, but most decay eventually returns nitrogen content to the atmosphere, as molecular nitrogen.
Nitrogen gas is acquired for industrial purposes by the fractional
distillation of liquid air, or by mechanical means using gaseous air (i.e. pressurised reverse
osmosis membrane or pressure swing adsorption). Commercial nitrogen is often a byproduct of air-processing for industrial concentration of oxygen for steelmaking and other purposes.
Molecular nitrogen (gas and liquid)
Nitrogen gas has a wide variety of applications, including serving as a more
inert replacement for air where
oxidation is undesirable;
* to preserve the freshness of packaged or bulk foods (by delaying
rancidity and other forms of oxidative damage)
* on top of liquid explosives for safety
* in the production of
electronic parts such as
transistors,
diodes, and
integrated circuits
* dried and pressurized, as a
dielectric gas for
high voltage equipment
* in the manufacture of
stainless steel* for filling automotive and aircraft
tires
due to its inertness and lack of
moisture or oxidative qualities, as opposed to air, though this is not necessary for consumer automobiles.
|
A computer rendering of the Nitrogen Molecule, N2. |
Contrary to some claims that nitrogen will diffuse more rapidly through rubber tires than air (and oxygen), nitrogen molecules are less likely to escape from the inside of a tire compared to the traditional air mixture used.
Air consists mostly of nitrogen and oxygen. Nitrogen molecules are larger than oxygen molecules and therefore, all else being equal, larger molecules diffuse through porous substances slower than smaller molecules.
A further example of its versatility is its use as a preferred alternative to
carbon dioxide to pressurize kegs of some
beers, particularly thicker and Scottish and English
ales, due to the smaller bubbles it produces, which make the dispensed beer smoother and headier. A modern application of a pressure sensitive nitrogen capsule known commonly as a "
widget" now allows nitrogen charged beers to be packaged in cans and bottles.
|
A tank of liquid nitrogen, used to supply a cryogenic freezer (for storing laboratory samples at a temperature of about -150 Celsius). |
Liquid nitrogen is produced industrially in large quantities by
fractional distillation of
liquid air and is often referred to by the quasi-formula
LN2 (but is more accurately written
N2(l) ). It is a
cryogenic fluid which can cause instant
frostbite on direct contact with living tissue. When appropriately
insulated from ambient
heat it serves as a compact and readily transported source of nitrogen gas without pressurization. Further, its ability to maintain temperatures far below the
freezing point of water as it boils at (77
K, -196 °
C or -320 °
F) makes it extremely useful in a wide range of applications as an open-cycle
refrigerant, including;
* the immersion freezing and transportation of
food products
* the
cryopreservation of
blood, reproductive cells (
sperm and
egg), and other
biological samples and materials (see
image at right)
* the
cryonic preservation of humans and pets in the hope of future revival with molecular repair technology
* in the study of
cryogenics* for demonstrations in
science education* as a
coolant for highly sensitive
sensors and low-noise
amplifiers
* in
dermatology for removing unsightly or potentially
malignant skin lesions such as
warts and
actinic keratosis* as a cooling supplement for
overclocking a
central processing unit, a
graphics processing unit, or another type of
computer hardware* as a cooling medium during machining of high strength materials.
* as a tool for thieves to freeze and then shatter locks or other security devices (such as chains)
Simple compounds
See also the category Nitrogen compounds.The main neutral
hydride of nitrogen is
ammonia (N
H3), although
hydrazine (N
2H
4) is also commonly used. Ammonia is more
basic than
water by 6 orders of magnitude. In
solution ammonia forms the
ammonium ion (NH
4+). Liquid ammonia (b.p. 240 K) is
amphiprotic (displaying either
Brønsted-Lowry acidic or basic character) and forms ammonium and less commonly)
amide ions (NH
2-); both amides and
nitride (N
3-)
salts are known, but
decompose in water. Singly, doubly, triply and quadruply substituted alkyl compounds of ammonia are called
amines (four substitutions, to form commercially and biologically important quarternary amines, results in a positively charged nitrogen, and thus a water-soluble, or at least
amphiphilic, compound). Larger chains, rings and structures of nitrogen hydrides are also known, but are generally unstable.
Other classes of nitrogen
anions (negatively charged ions) are
azides (N
3-), which are linear and
isoelectronic to
carbon dioxide. Another
molecule of the same structure is
dinitrogen monoxide (N
2O), also known as laughing gas. This is one of a variety of
oxides, the most prominent of which are
nitrogen monoxide (NO) (known more commonly as
nitric oxide in biology) 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, and is a fairly strong
oxidizing agent.
Nitrogen can also be found in
organic compounds. Common nitrogen
functional groups include:
amines,
amides,
nitro groups,
imines, and
enamines. The amount of nitrogen in a
chemical substance can be determined by the
Kjeldahl method.
Nitrogen compounds of notable economic importance
Molecular nitrogen in the atmosphere is relatively non-reactive due to its strong bond, and the (N
2) plays an inert role in the human body, being neither produced or destroyed. In nature, nitrogen is slowly converted into biologically (and industrially) useful compounds by some living organisms, notably certain
bacteria (i.e.
nitrogen fixing bacteria - see
Biological role above). Molecular nitrogen is also released into the atmosphere in the process of decay, in dead plant and animal tissues. The ability to combine or
fix molecular nitrogen is a key feature of modern industrial chemistry, where nitrogen and
natural gas are converted into
ammonia via the
Haber process. Ammonia, in turn, can be used directly (primarily as a
fertilizer, and in the synthesis of nitrated fertilizers), or as a precursor of many other important materials including
explosives, largely via the production of
nitric acid by the
Ostwald process.
The
salts of nitric acid include important compounds such as
potassium nitrate (or
saltpeter, important historically for its use in
gunpowder) and
ammonium nitrate, an important fertilizer and explosive (see
ANFO). Various other nitrated organic compounds, such as
nitroglycerin and
trinitrotoluene, and
nitrocellulose, are used as explosives and propellants for modern firearms. Nitric acid is used as an
oxidizing agent in liquid fueled
rockets.
Hydrazine and hydrazine derivatives find use as rocket
fuels. In all of these compounds, the basic instability and tendency to burn or explode is derived from the fact that nitrogen is present as an oxide, and not as the far more stable nitrogen molecule (N
2) which is a product of the compound's decomposition. When nitrates burn or explode, the formation of the powerful triple bond in the (N
2) which results, produces most of the energy of the reaction.
Nitrogen is a constituent of molecules in every major drug class in pharmacology and medicine.
Nitrous oxide (N
20) was discovered early in the 19th century to be a partial anesthetic, though it was not used as a surgical anesthetic until later. Called "
laughing gas", it was found capable of inducing a state of social disinhibition resembling drunkenness. Other notable nitrogen-containing drugs are drugs derived from plant
alkaloids, such as
morphine (there exist many alkaloids known to have pharmacological effects; in some cases they appear natural chemical defences of plants against predation). Nitrogen containing drugs include all of the major classes of antibiotics, and organic nitrate drugs like
nitroglycerin and
nitroprusside which regulate blood pressure and heart action by mimicing the action of
nitric oxide.
Rapid release of nitrogen gas into an enclosed space can displace oxygen, and therefore represents an
asphyxiation hazard. An example occurred shortly before the launch of the first Space Shuttle mission in
1981, when two technicians were killed in a space located in the Shuttle's
Mobile Launch Platform that was pressurized with pure nitrogen as a precaution against fire.
When breathed at high
partial pressures (more than about 3 atmospheres, encountered at depths below about 30 m in diving) nitrogen begins to act as an anesthetic agent. As such, it can cause
nitrogen narcosis, a temporary semi-anesthetized condition of mental impairment similar to that caused by
nitrous oxide.
Nitrogen also dissolves in the
bloodstream, and rapid decompression (particularly in the case of divers ascending too quickly, or astronauts decompressing too quickly from cabin pressure to spacesuit pressure) can lead to a potentially fatal condition called
decompression sickness (formerly known as caisson sickness or more commonly, the "bends"), when nitrogen bubbles form in the bloodstream.
Direct skin contact with liquid nitrogen causes severe frostbite (cryogenic burns) within moments to seconds, depending on form of liquid nitrogen (liquid vs. mist) and surface area of the nitrogen-soaked material (soaked clothing or cotton causing more rapid damage than a spill of direct liquid to skin, which for a few seconds is protected by the
Leidenfrost effect ).
*
Nutrient*
Nitrogen cycle*
NOx*
Nitrous oxide*
Los Alamos National Laboratory – Nitrogen*
Chemistry of the Elements, N. N. Greenwood and A. Earnshaw. ISBN 0-08-022057-6
*
Biochemistry, R.H. Garrett and C.M. Grisham. 2nd edition, 1999. ISBN 0-03-022318-0
*
Why high nitrogen density in explosives?*
WebElements.com – Nitrogen*
It's Elemental – Nitrogen*
Schenectady County Community College – Nitrogen*
Nitrogen N2 Properties, Uses, Applications*
Computational Chemistry Wiki*
Handling procedures for liquid nitrogen*
Material Safety Data Sheet
