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15 novembre 2011 2 15 /11 /novembre /2011 02:51

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere. The element nitrogen was discovered as a separable component of air, by Scottish physician Daniel Rutherford, in 1772.Sony VAIO VPCF116FGBI Battery

Many industrially important compounds, such as ammonia, nitric acid, organic nitrates (propellants and explosives), andcyanides, contain nitrogen. The extremely strong bond in elemental nitrogen dominates nitrogen chemistry, causing difficulty for both organisms and industry in breaking the bond to convert the N2 into useful compounds,Sony VAIO VPCF117FJ/W Battery

but at the same time causing release of large amounts of often useful energy when the compounds burn, explode, or decay back into nitrogen gas.

Nitrogen occurs in all living organisms, and the nitrogen cycle describes movement of the element from the air into thebiosphere and organic compounds, then back into the atmosphere. Sony VAIO VPCF117HG/BI Battery

Synthetically produced nitrates are key ingredients of industrial fertilizers, and also key pollutants in causing the eutrophication of water systems. Nitrogen is a constituent element of amino acids and thus of proteins and nucleic acids (DNA and RNA). It resides in the chemical structure of almost all neurotransmitters, and is a defining component of alkaloids, biological molecules produced by many organisms.Sony VAIO VPCF118FJ/W Battery

The human body contains about 3% by weight of nitrogen, a larger fraction than all elements save oxygen, carbon, and hydrogen.


Nitrogen is formally considered to have been discovered by Daniel Rutherford in 1772, who called it noxious air or fixed air.Sony VAIO VPCF119FC Battery

The fact that there was an element of air that does not support combustion was clear to Rutherford. Nitrogen was also studied at about the same time by Carl Wilhelm Scheele, Henry Cavendish, and Joseph Priestley, who referred to it as burnt airor phlogisticated air.Sony VAIO VPCF119FC/BI Battery

Nitrogen gas was inert enough that Antoine Lavoisier referred to it as "mephitic air" or azote, from the Greek word ?????? (azotos) meaning "lifeless". In it, animals died and flames were extinguished. Lavoisier's name for nitrogen is used in many languages (French, Polish, Russian, etc.) and still remains in English in the common names of many compounds, such as hydrazine and compounds of the azide ion.Sony VAIO VPCF119FJ/BI Battery

The English word nitrogen (1794) entered the language  from the French nitrogène, coined in 1790 by French chemist Jean Antoine Chaptal (1756–1832), from "nitre" + Fr. gène "producing" (from Gk. -????? means "forming" or "giving birth to."). The gas had been found in nitric acid.Sony VAIO VPCF11AFJ Battery

Chaptal's meaning was that nitrogen gas is the essential part of nitric acid, in turn formed from saltpetre (potassium nitrate), then known as nitre. However, this word in the more ancient world originally described sodium salts that did not contain nitrate, and is a cognate of natron and nitron.Sony VAIO VPCF11AGJ Battery

Nitrogen compounds were well known during the Middle Ages. 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).Sony VAIO VPCF11AHJ Battery

The earliest military, industrial, and agricultural applications of nitrogen compounds involved uses saltpetre (sodium nitrate or potassium nitrate), the most notable in gunpowder, and later as fertilizer. In 1910, Lord Rayleigh discovered that an electrical discharge in nitrogen gas produced "active nitrogen", an allotrope considered to bemonatomic.Sony VAIO VPCF11JFX/B Battery

The "whirling cloud of brilliant yellow light" produced by his apparatus reacted with quicksilver to produce explosive mercury nitride.


Nitrogen is a nonmetal, with an electronegativity of 3.04. It has five electrons in its outer shell and is, therefore,trivalent in most compounds. Sony VAIO VPCF11M1E Battery

The triple bond in molecular nitrogen (N2) is one of the strongest. The resulting difficulty of converting N2 into other compounds, and the ease (and associated high energy release) of converting nitrogen compounds into elemental N2, have dominated the role of nitrogen in both nature and human economic activities.Sony VAIO VPCF11M1E/H Battery

At atmospheric pressure molecular nitrogen condenses (liquefies) at 77 K (?195.79 °C) and freezes at 63 K (?210.01 °C)[1]into the beta hexagonal close-packed crystal allotropic form. Below 35.4 K (?237.6 °C) nitrogen assumes the cubic crystal allotropic form (called the alpha-phase).Sony VAIO VPCF11MFX/B Battery

Liquid nitrogen, a fluid resembling water in appearance, but with 80.8% of the density (the density of liquid nitrogen at its boiling point is 0.808 g/mL), is a common cryogen.

Unstable allotropes of nitrogen consisting of more than two nitrogen atoms have been produced in the laboratory, like N3andN4.Sony VAIO VPCF11S1E Battery

Under extremely high pressures (1.1 million atm) and high temperatures (2000 K), as produced using a diamond anvil cell, nitrogen polymerizes into the single-bonded cubic gauche crystal structure. This structure is similar to that ofdiamond, and both have extremely strong covalent bonds. N4 is nicknamed "nitrogen diamond." Sony VAIO VPCF11S1E/B Battery

Other (as yet unsynthesized) allotropes include hexazine (N6, a benzene analog)  and octaazacubane (N8, a cubane analog).The former is predicted to be highly unstable, while the latter is predicted to be stable, for reasons of orbital symmetry.


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. Sony VAIO VPCF11Z1E Battery

Of the ten isotopes produced synthetically, 13N has a half-life of ten minutes and the remaining isotopes have half-lives on the order of seconds or less. Biologically mediated reactions (e.g., assimilation, nitrification, anddenitrification) strongly control nitrogen dynamics in the soil. These reactions typically result in 15N enrichment of thesubstrate and depletion of the product.Sony VAIO VPCF11Z1E/BI Battery

A small part (0.73%) of the molecular nitrogen in Earth's atmosphere is the isotopologue 14N15N, and almost all the rest is14N2.

Radioisotope 16N is the dominant radionuclide in the coolant of pressurized water reactors or boiling water reactors during normal operation. It is produced from 16O (in water) via (n,p) reaction. It has a short half-life of about 7.1 s, but during its decay back to 16O produces high-energy gamma radiation (5 to 7 MeV).Sony VAIO VPCF11ZHJ Battery

Because of this, the access to the primary coolant piping in a pressurized water reactor must be restricted during reactor power operation.16N is one of the main means used to immediately detect even small leaks from the primary coolant to the secondary steam cycle.Sony VAIO VPCF127HGBI Battery

In similar fashion, access to any of the steam cycle components in a boiling water reactor nuclear power plant must be restricted during operation. Condensate from the condenser is typically retained for 10 minutes to allow for decay of the 16N. This eliminates the need to shield and restrict access to any of the feed water piping or pumps.Sony VAIO VPCF137HG/BI Battery

Electromagnetic spectrum

Molecular nitrogen (14N2) is largely transparent to infrared and visible radiation because it is a homonuclear molecule and, thus, has no dipole moment to couple to electromagnetic radiation at these wavelengths. Significant absorption occurs at extreme ultraviolet wavelengths, beginning around 100 nanometers.Sony VAIO VPCS111FM/S Battery
This is associated with electronic transitions in the molecule to states in which charge is not distributed evenly between nitrogen atoms. Nitrogen absorption leads to significant absorption of ultraviolet radiation in the Earth's upper atmosphere and the atmospheres of other planetary bodies. Sony VAIO VPCS115EC Battery
For similar reasons, pure molecular nitrogen lasers typically emit light in the ultraviolet range.

Nitrogen also makes a contribution to visible air glow from the Earth's upper atmosphere, through electron impact excitation followed by emission. This visible blue air glow (seen in the polar aurora and in the re-entry glow of returning spacecraft) typically results not from molecular nitrogen but rather from free nitrogen atoms combining with oxygen to form nitric oxide (NO).Sony VAIO VPCS115FG Battery

Nitrogen gas also exhibits scintillation.


In general, nitrogen is unreactive at standard temperature and pressure. N2 reacts spontaneously with few reagents, being resilient to acids andbases as well as oxidants and most reductants. Sony VAIO VPCS117GG Battery

When nitrogen reacts spontaneously with a reagent, the net transformation is often callednitrogen fixation.

Nitrogen reacts with elemental lithium.  Lithium burns in an atmosphere of N2 to give lithium nitride:

6 Li + N2 ? 2 Li3N

Magnesium also burns in nitrogen, forming magnesium nitride.Sony VAIO VPCS117GGB Battery

3 Mg + N2 ? Mg3N2

N2 forms a variety of adducts with transition metals. The first example of a dinitrogen complex is [Ru(NH3)5(N2)]2+ (see figure at right). Such compounds are now numerous, other examples include IrCl(N2)(PPh3)2, W(N2)2(Ph2PCH2CH2PPh2)2, and [(?5-C5Me4H)2Zr]2(?2, ?2,?2-N2).Sony VAIO VPCS118EC Battery

These complexes illustrate how N2 might bind to the metal(s) in nitrogenase and the catalyst for theHaber process.[13] A catalytic process to reduce N2 to ammonia with the use of a molybdenum complex in the presence of a proton source was published in 2005.Sony VAIO VPCS119FJ/B Battery

The starting point for industrial production of nitrogen compounds is the Haber process, in which nitrogen is fixed by reacting N2and H2 over an iron(III) oxide (Fe3O4) catalyst at about 500 °C and 200 atmospheres pressure. Biological nitrogen fixation in free-living cyanobacteria and in the root nodules of plants also produces ammonia from molecular nitrogen.Sony VAIO VPCS119GC Battery

The reaction, which is the source of the bulk of nitrogen in the biosphere, is catalyzed by the nitrogenase enzyme complex that contains Fe and Mo atoms, using energy derived from hydrolysis of adenosine triphosphate (ATP) into adenosine diphosphate and inorganic phosphate (?20.5 kJ/mol).Sony VAIO VPCS11AFJ Battery


Nitrogen is the largest single constituent of the Earth's atmosphere (78.082% by volume of dry air, 75.3% by weight in dry air). It is created by fusion processes in stars, and is estimated to be the seventh most abundant chemical element by mass in the universe.Sony VAIO VPCS11AGJ Battery

Molecular nitrogen and nitrogen compounds have been detected in interstellar space by astronomers using the Far Ultraviolet Spectroscopic Explorer. Molecular nitrogen is a major constituent of the Saturnian moon Titan's thick atmosphere, and occurs in slightly appreciable to trace amounts in other planetary atmospheres.Sony VAIO VPCS11AHJ Battery

Nitrogen is present in all living organisms, in proteins, nucleic acids, and other molecules. It typically makes up around 4% of the dry weight of plant matter, and around 3% of the weight of the human body. It is a large component of animal waste (for example, guano), usually in the form of urea, uric acid, ammonium compounds, and derivatives of these nitrogenous products, which are essential nutrients for all plants that cannot fix atmospheric nitrogen.Sony VAIO VPCS11AVJ Battery

Nitrogen occurs naturally in many minerals, such as saltpetre (potassium nitrate), Chile saltpetre (sodium nitrate) and sal ammoniac (ammonium chloride). Most of these are uncommon, partly because of the minerals' ready solubility in water. See also Nitrate minerals and Ammonium minerals.Sony VAIO VPCS11J7E/B Battery


The main neutral hydride of nitrogen is ammonia (NH3), although hydrazine (N2H4) is also commonly used. Ammonia is more basic than water by 6 orders of magnitude. Insolution ammonia forms the ammonium ion (NH+
4). Sony VAIO VPCS11M1E/W Battery

Liquid ammonia (boiling point 240 K) is amphiprotic (displaying either Brønsted-Lowry acidic or basic character) and forms ammonium and the less common amide ions (NH?
2); both amides and nitride (N3?) salts are known, but decompose in water. Singly, doubly, triply and quadruply substituted alkyl compounds of ammonia are called amines Sony VAIO VPCS11V9E Battery

(four substitutions, to form commercially and biologically important quaternary 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.Sony VAIO VPCS11V9E/B Battery

Other classes of nitrogen anions (negatively charged ions) are the poisonous azides (N?
3), which are linear and isoelectronic to carbon dioxide, but which bind to important iron-containing enzymes in the body in a manner more resembling cyanide.Sony VAIO VPCS11X9E/B Battery

Another molecule of the same structure is the colorless and relatively inert anesthetic gas Nitrous oxide (dinitrogen monoxide, N2O), also known as laughing gas. This is one of a variety of nitrogen oxides that form a family often abbreviated as NOx.Sony VAIO VPCS123FGB Battery

Nitric oxide (nitrogen monoxide, NO), is a natural free radical used in signal transduction in both plants and animals, for example, in vasodilation by causing the smooth muscle of blood vessels to relax. The reddish and poisonous nitrogen dioxide NO2 contains an unpaired electron and is an important component ofsmog. Sony VAIO VPCS125EC Battery

Nitrogen molecules containing unpaired electrons show a tendency to dimerize (thus pairing the electrons), and are, in general, highly reactive. The corresponding acids are nitrous HNO2 and nitric acid HNO3, with the corresponding salts called nitrites and nitrates.Sony VAIO VPCS128EC Battery

The higher oxides dinitrogen trioxide N2O3, dinitrogen tetroxide N2O4 and dinitrogen pentoxide N2O5, are unstable and explosive, a consequence of the chemical stability of N2. Nearly every hypergolic rocket engine uses N2O4 as the oxidizer; their fuels, various forms of hydrazine, are also nitrogen compounds. Sony VAIO VPCS129GC Battery

These engines are extensively used on spacecraft such as the space shuttle and those of the Apollo Program because their propellants are liquids at room temperature and ignition occurs on contact without an ignition system, allowing many precisely controlled burns. Sony VAIO VPCS12C7E/B Battery

Some launch vehicles such as the Titan II and Ariane 1 through 4 also use hypergolic fuels, although the trend is away from such engines for cost and safety reasons. N2O4 is an intermediate in the manufacture of nitric acid HNO3, one of the few acids stronger than hydronium and a fairly strong oxidizing agent.Sony VAIO VPCS12L9E/B Battery

Nitrogen is notable for the range of explosively unstable compounds that it can produce. Nitrogen triiodide NI3 is an extremely sensitive contact explosive.Nitrocellulose, produced by nitration of cellulose with nitric acid, is also known as guncotton.Sony VAIO VPCS12V9E/B Battery

Nitroglycerin, made by nitration of glycerin, is the dangerously unstable explosive ingredient of dynamite. The comparatively stable, but more powerful explosive trinitrotoluene (TNT) is the standard explosive against which the power of nuclear explosions are measured.Sony VAIO VPCY115FGS Battery

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.Sony VAIO VPCY115FX/BI Battery

Production and applications

Nitrogen gas is an industrial gas produced by the fractional distillation of liquid air, or by mechanical means using gaseous air (i.e., pressurized 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.Sony VAIO VPCY115FXBI Battery

When supplied compressed in cylinders it is often called OFN (oxygen-free nitrogen).

Nitrogen gas has a variety of applications, including serving as an inert replacement for air where oxidation is undesirable;

  • As a modified atmosphere, pure or mixed with carbon dioxide, to preserve the freshness of packaged or bulk foods (by delaying rancidityand other forms of oxidative damage)Sony VAIO VPCY118EC Battery
  • In ordinary incandescent light bulbs as an inexpensive alternative to argon.
  • The production of electronic parts such as transistors, diodes, and integrated circuits
  • Dried and pressurized, as a dielectric gas for high-voltage equipment
  • The manufacturing of stainless steel
  • Used in military aircraft fuel systems to reduce fire hazard, (see inerting system)
  • On top of liquid explosives as a safety measure Sony VAIO VPCY118GX/BI Battery
  • Filling automotive and aircraft tires  due to its inertness and lack of moisture or oxidative qualities, as opposed to air. Growing in popularity for consumer vehicles due to ability to enhance fuel efficiency, increase tire longevity, and provide more safety and stability. Sony VAIO VPCY119FJ/S Battery
  • This has not yet been independently verified in the case of consumer vehicles which don't have such high loads on their tires. The difference in N2 content between air and pure N2 is 20%
  • Used as a propellant for draught wine, and as an alternative to or together with carbon dioxide for other beverages.Sony VAIO VPCY11AFJ Battery

Nitrogen is commonly used during sample preparation procedures for chemical analysis. To be specific, it is used to concentrate and reduce the volume of liquid samples. Directing a pressurized stream of nitrogen gas perpendicular to the surface of the liquid allows the solvent to evaporate while leaving the solute(s) and un-evaporated solvent behind.Sony VAIO VPCY11AGJ Battery

Nitrogen tanks are also replacing carbon dioxide as the main power source for paintball guns. The downside is that nitrogen must be kept at higher pressure than CO2, making N2 tanks heavier and more expensive.

Nitrogenated beer

A further example of its versatility is its use as a preferred alternative to carbon dioxide to pressurize kegs of some beers, Sony VAIO VPCY11AHJ Battery

in particular, stouts and Britishales, 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.Sony VAIO VPCY11AVJ Battery

A mixture of nitrogen and carbon dioxide can be used for this purpose as well, to maintain the saturation of beer with carbon dioxide.

Liquid nitrogen

Liquid nitrogen is a cryogenic liquid. At atmospheric pressure, it boils at ?195.8 °C. When insulated in proper containers such as Dewar flasks, it can be transported without much evaporative loss.Sony VAIO VPCY11M1E/S Battery

Like dry ice, the main use of liquid nitrogen is as a refrigerant. Among other things, it is used in the cryopreservation of blood, reproductive cells (sperm and egg), and other biological samples and materials. It is used in the clinical setting incryotherapy to remove cysts and warts on the skin.Sony VAIO VPCY11S1E Battery

It is used in cold traps for certain laboratory equipment and to cool X-ray detectors. It has also been used to cool central processing units and other devices in computers that are overclocked, and that produce more heat than during normal operation.Sony VAIO VPCY11V9E/S Battery

Applications of nitrogen compounds

Molecular nitrogen (N2) in the atmosphere is relatively non-reactive due to its strong bond, and N2 plays an inert role in the human body, being neither produced nor destroyed. In nature, nitrogen is converted into biologically (and industrially) useful compounds by lightning, Sony VAIO VPCY218EC/BI Battery

and by some living organisms, notably certain bacteria (i.e. nitrogen fixing bacteria – see Biological role below). Molecular nitrogen is 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 theHaber process. Sony VAIO VPCY218EC/G Battery

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 organic and inorganic salts of nitric acid have been important historically as convenient stores of chemical energy.Sony VAIO VPCY218EC/L Battery

They include important compounds such aspotassium nitrate (or saltpeter used in gunpowder) and ammonium nitrate, an important fertilizer and explosive (see ANFO). Various other nitrated organic compounds, such as nitroglycerin, trinitrotoluene, and nitrocellulose, are used as explosives and propellants for modern firearms.Sony VAIO VPCY218EC/P Battery

Nitric acid is used as an oxidizing agent in liquid fueled rockets. Hydrazine and hydrazine derivatives find use as rocket fuels and monopropellants. In most 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 (N2), which is a product of the compounds' thermal decomposition.Sony VAIO VPCY21S1E/L Battery

When nitrates burn or explode, the formation of the powerful triple bond in the N2 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 (N2O) was discovered early in the 19th century to be a partial anesthetic, though it was not used as a surgical anesthetic until later.Sony VAIO VPCY21S1E/P Battery

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 defenses of plants against predation). Sony VAIO VPCY21S1E/SI Battery

Drugs that contain nitrogen include all major classes of antibiotics and organic nitrate drugs like nitroglycerin and nitroprusside that regulate blood pressure and heart action by mimicking the action ofnitric oxide.

Biological role

Nitrogen is an essential building block of amino and nucleic acids, essential to life on Earth.Sony VAIO VPCCW2S5C CN1 Battery

Elemental nitrogen in the atmosphere cannot be used directly by either plants or animals, and must be converted to a reduced (or 'fixed') state in order to be useful for higher plants and animals. Precipitation often contains substantial quantities of ammonium and nitrate, thought to result from nitrogen fixation by lightning and other atmospheric electric phenomena.Sony VAIO VPCEA20 Battery

This was first proposed by Liebig in 1827 and later confirmed. However, because ammonium is preferentially retained by the forest canopy relative to atmospheric nitrate, most fixed nitrogen reaches the soil surface under trees as nitrate. Soil nitrate is preferentially assimilated by tree roots relative to soil ammonium .Sony VAIO VPCEB10 Battery

Specific bacteria (e.g., Rhizobium trifolium) possess nitrogenase enzymes that can fix atmospheric nitrogen (see nitrogen fixation) into a form (ammonium ion) that is chemically useful to higher organisms. This process requires a large amount of energy and anoxic conditions. Sony VAIO VPCEB11FM Battery

Such bacteria may live freely in soil (e.g.,Azotobacter) but normally exist in a symbiotic relationship in the root nodules of leguminous plants (e.g. clover, Trifolium, or soybean plant, Glycine max). Nitrogen-fixing bacteria are also symbiotic with a number of unrelated plant species such as alders (Alnus) spp., lichens, Casuarina, Myrica, liverworts, andGunnera.Sony VAIO VPCEB11FM/BI Battery

As part of the symbiotic relationship, the plant converts the 'fixed' ammonium ion to nitrogen oxides and amino acids to form proteins and other molecules, (e.g.,alkaloids). In return for the 'fixed' nitrogen, the plant secretes sugars to the symbiotic bacteria. Legumes maintain an anaerobic (oxygen free) environment for their nitrogen-fixing bacteria.Sony VAIO VPCEB11FM/T Battery

Plants are able to assimilate nitrogen directly in the form of nitrates that 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.Sony VAIO VPCEB11FM/WI Battery

Nitrogen compounds are basic building blocks in animal biology as well. 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. Sony VAIO VPCEB11FX Battery

Plant-feeding insects are dependent on nitrogen in their diet, such that varying the amount of nitrogen fertilizer applied to a plant can affect the reproduction rate of insects feeding on fertilized plants.

Soluble nitrate is an important limiting factor in the growth of certain bacteria in ocean waters.Sony VAIO VPCEB11FX/BI Battery

In many places in the world, artificial fertilizers applied to crop-lands to increase yields result in run-off delivery of soluble nitrogen to oceans at river mouths. This process can result in eutrophication of the water, as nitrogen-driven bacterial growth depletes water oxygen to the point that all higher organisms die. Sony VAIO VPCEB11FX/T Battery

Well-known "dead zone" areas in the U.S. Gulf Coast and the Black Sea are due to this important polluting process.

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.Sony VAIO VPCEB11FX/WI Battery

In animals, free radical nitric oxide (NO) (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, in general, results in excretion of urea, while animal metabolism of nucleic acids results in excretion of urea and uric acid. Sony VAIO VPCEB11GX Battery

The characteristic odor of animal flesh decay is caused by the creation of long-chain, nitrogen-containing amines, such as putrescine and cadaverine, which are breakdown products of the amino acids ornithine and lysine, respectively, in decaying proteins.

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.Sony VAIO VPCEB11GX/BI Battery

The circulation of nitrogen from atmosphere, to organic compounds, then back to the atmosphere, is referred to as the nitrogen cycle.


Rapid release of nitrogen gas into an enclosed space can displace oxygen, and therefore represents an asphyxiation hazard. Sony VAIO VPCEB11GX/T Battery

This may happen with few warning symptoms, since the human carotid body is a relatively slow and a poor low-oxygen (hypoxia) sensing system. An example occurred shortly before the launch of the first Space Shuttle mission in 1981, when two technicians lost consciousness (and one of them died) after they walked into a space located in the Shuttle's Mobile Launcher Platform that was pressurized with pure nitrogen as a precaution against fire. Sony VAIO VPCEB11GX/WI Battery

The technicians would have been able to exit the room if they had experienced early symptoms from nitrogen-breathing.

When inhaled at high partial pressures (more than about 4 bar, encountered at depths below about 30 m in scuba diving), nitrogen begins to act as an anesthetic agent. It can cause nitrogen narcosis, a temporary semi-anesthetized state of mental impairment similar to that caused by nitrous oxide.Sony VAIO VPCEB12FX Battery

Nitrogen also dissolves in the bloodstream and body fats. Rapid decompression (in particular, 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 the bends), Sony VAIO VPCEB12FX/BI Battery

when nitrogen bubbles form in the bloodstream, nerves, joints, and other sensitive or vital areas.Other "inert" gases (those gases other than carbon dioxide and oxygen) cause the same effects from bubbles composed of them, so replacement of nitrogen in breathing gases may prevent nitrogen narcosis, but does not prevent decompression sickness.Sony VAIO VPCEB12FX/BIC Battery

Direct skin contact with liquid nitrogen will cause severe frostbite (cryogenic "burns"). This may happen almost instantly on contact, or after a second or more, depending on the form of liquid nitrogen. Bulk liquid nitrogen causes less rapid freezing than a spray of nitrogen mist (such as is used to freeze certain skin growths in the practice of dermatology). Sony VAIO VPCEB12FX/T Battery

The extra surface area provided by nitrogen-soaked materials is also important, with soaked clothing or cotton causing far more rapid damage than a spill of direct liquid to skin. Full "contact" between naked skin and large collected-droplets or pools of liquid nitrogen may be prevented for a second or two, by a layer of insulating gas from the Leidenfrost effect. Sony VAIO VPCEB14FX Battery

This may give the skin a second of protection from nitrogen bulk liquid. However, liquid nitrogen applied to skin in mists, and on fabrics, bypasses this effect, and causes local frostbite immediately.

Nitrogen asphyxiation is an occasional cause of accidental death and a theoretical method of capital punishment advocated in a National Review article, "Killing with kindness – capital punishment by nitrogen asphyxiation" (Creque 1995). Sony VAIO VPCEB14FX/BI Battery

The painful experience of suffocation is not caused by lack of oxygen, but rather because of a buildup of carbon dioxide in the bloodstream which is exhaled under normal circumstances.

When humans breathe in pure nitrogen, they exhale carbon dioxide without resupplying oxygen. Nitrogen is a colorless, odorless and tasteless gas that constitutes approximately 78 percent of the Earth's atmosphere.Sony VAIO VPCEB14FX/T Battery

As such, the subject would detect no abnormal sensation. This leads to asphyxiation without the painful and traumatic feeling of suffocation. Because of this property, nitrogen in Hebrew is called ???? ("asphyxiator"),in German is called "Stickstoff", in Dutch "stikstof", ("suffocation matter") - Sony VAIO VPCEB14FX/WI Battery

the Scandinavian languages call it "kväve", "kvælstof" and "kvelstoff" from "kväva/kvele/kvæle" ("to asphyxiate"), in Russian "????" ("not life-friendly"), in Croatian "dušik" (from the now archaic word "dušiti", meaning "to asphyxiate").

For this reason, accidental nitrogen asphyxiation is a possible hazard where large quantities of nitrogen are used.Sony VAIO VPCEB15FM Battery

Also, deliberate nitrogen asphyxiation is viewed by some as a more humane way to end a human life in a controlled setting. As the principal component in air, nitrogen poses no significant risk upon discharge.

As an execution method

Although execution by nitrogen asphyxiation was discussed briefly in print in 1995 (Creque), it is not used by any nation.Sony VAIO VPCEB15FM/BI Battery

In a televised documentary in 2007, the UK political commentator (and former Member of Parliament United Kingdom), Michael Portillo examined execution techniques in use around the world and found them unsatisfactory; his conclusion was that nitrogen asphyxiation would be the best method.Sony VAIO VPCEB15FM/T Battery

Accidental deaths

Accidental nitrogen asphyxiation causes about 8 deaths per year in the United States, which is asserted to be more than from any other industrial gas. For example in 1981, shortly before the launch of the first Space Shuttle mission, two technicians lost consciousness and one of them died after they entered the Orbiter aft compartment which was pressurized with pure nitrogen as a precaution against fire. Sony VAIO VPCEB15FM/WI Battery

A laboratory assistant died in Scotland in 1999, apparently from asphyxiation, after liquid nitrogen spilled in a basement storage room.


A typical human breathes between 12 and 20 times per minute at a rate primarily influenced by carbon dioxide concentration, and thus pH, in the blood. Sony VAIO VPCEB15FX Battery

With each breath, a volume of about 0.6 liters is exchanged from an active lung volume (tidal volume + functional residual capacity) of about 3 liters. Normal Earth atmosphereis about 78 percent nitrogen, 21 percent oxygen, and 1 percent argon, carbon dioxide, and other gases. Sony VAIO VPCEB15FX/BI Battery

After just two or three breaths of nitrogen, the oxygen concentration in the lungs would be low enough for some oxygen already in the bloodstream to exchange back to the lungs and be eliminated by exhalation. Crude simulation of oxygen transport through the lungs and blood stream suggests that the partial pressure of oxygen in arterial blood would be about 50 percent of saturation 1 minute after switching gases and would reach zero within 3 minutes.Sony VAIO VPCEB15FX/T Battery

Unconsciousness in cases of accidental asphyxia can occur within 1 minute. Loss of consciousness results from critical hypoxia, when arterial oxygen saturation is less than 60% (Fisher n.d.). “At oxygen concentrations [in air] of 4 to 6%, there is loss of consciousness in 40 seconds and death within a few minutes” (DiMaio & DiMaio 2001:231).Sony VAIO VPCEB15FX/WI Battery

As this procedure provides an atmosphere completely devoid of oxygen, the sequence of effects should be expected to occur even more quickly. At an altitude greater than 43,000 ft (13,000 m), where the ambient oxygen concentration is equivalent to 3.6% at sea level, an average individual is able to perform flying duties efficiently for only 9 to 12 seconds without oxygen supplementation (Fisher n.d.). Sony VAIO VPCEB16FX Battery

The US Air Force trains air crews to recognize their individual subjective signs of approaching hypoxia. Some individuals experience headache, dizziness, fatigue, nausea, or euphoria, but some become unconscious without warning (Fisher n.d.). Equivalent training is unlikely for a condemned individual, making unconsciousness without warning probable, although as much as a 30 second warning is possible.Sony VAIO VPCEB16FX/B Battery

Loss of consciousness may be accompanied by convulsions (Fisher n.d.) and is followed by cyanosis and cardiac arrest. About 7 minutes of oxygen deprivation causesdeath of the cerebral cortex and presumably the medulla oblongata, which controls breathing and heart action.Sony VAIO VPCEB16FX/G Battery

A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and u

sed as energy. Sony VAIO VPCEB16FX/L Battery

Methods for nutrient intake vary, with animals and protists consuming foods that are digested by an internal digestive system, but most plants ingest nutrients directly from the soil through their roots or from the atmosphere.

Organic nutrients include carbohydrates, fats, proteins (or their building blocks, amino acids), and vitamins. Sony VAIO VPCEB16FX/P Battery

Inorganic chemical compounds such as dietary minerals, water, and oxygen may also be considered nutrients. A nutrient is said to be "essential" if it must be obtained from an external source, either because the organism cannot synthesize it or produces insufficient quantities. Sony VAIO VPCEB16FX/W Battery

Nutrients needed in very small amounts are micronutrients and those that are needed in larger quantities are called macronutrients. The effects of nutrients are dose-dependent and shortages are called deficiencies.

See healthy diet for more information on the role of nutrients in human nutrition.Sony VAIO VPCEB17FX Battery

Macronutrients is defined in several different ways.

  • The chemical elements humans consume in the largest quantities are carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulphur, or CHNOPS.Sony VAIO VPCEB17FX/B Battery
  • The classes of chemical compounds humans consume in the largest quantities and which provide bulk energy are carbohydrates, proteins, and fats. Water and atmospheric oxygen also must be consumed in large quantities, but are not always considered "food" or "nutrients".Sony VAIO VPCEB17FX/G Battery
  • Calcium, salt (sodium and chloride), magnesium, and potassium (along with phosphorus and sulfur) are sometimes added to the list of macronutrients because they are required in large quantities compared to other vitamins and minerals. They are sometimes referred to as the macrominerals.Sony VAIO VPCEB17FX/L Battery

Substances that provide energy

  • Carbohydrates are compounds made up of types of sugars. Carbohydrates are classified by their number of sugar units: monosaccharides (such as glucose andfructose), disaccharides (such as sucrose and lactose), oligosaccharides, and polysaccharides (such as starch, glycogen, and cellulose).Sony VAIO VPCEB17FX/P Battery
  • Proteins are organic compounds that consist of the amino acids joined by peptide bonds. The body cannot manufacture some of the amino acids (termed essential amino acids); the diet must supply these. In nutrition, proteins are broken down through digestion by proteases back into free amino acids.Sony VAIO VPCEB17FX/W Battery
  • Fats consist of a glycerin molecule with three fatty acids attached. Fatty acids are unbranched hydrocarbon chains, connected by single bonds alone (saturated fatty acids) or by both double and single bonds (unsaturated fatty acids). Fats are needed to keep cell membranes functioning properly,Sony VAIO VPCEB190X Battery
  • to insulate body organs against shock, to keep body temperature stable, and to maintain healthy skin and hair. The body does not manufacture certain fatty acids (termed essential fatty acids) and the diet must supply these.

Fat has an energy content of 9 kcal/g (~37.7 kJ/g); proteins and carbohydrates 4 kcal/g (~16.7 kJ/g). Ethanol (grain alcohol) has an energy content of 7 kcal/g (~29.3 kJ/g).Sony VAIO VPCEB19FX Battery

Substances that support metabolism

  • Dietary minerals are generally trace elements, salts, or ions such as copper and iron. Some of these minerals are essential to human metabolism.
  • Vitamins are organic compounds essential to the body. They usually act as coenzymes or cofactors for various proteins in the body.Sony VAIO VPCEB19GX Battery
  • Water is an essential nutrient and is the solvent in which all the chemical reactions of life take place.

Plants absorb nutrients from the soil or the atmosphere, or from water (mainly aquatic plants) an exception are the carnivorous plants, which externally digest nutrients from animals, before ingesting them.Sony VAIO VPCEB1AFX Battery

The chemical elements consumed in the greatest quantities by plants are carbon, hydrogen, and oxygen. These are present in the environment in the form of water and carbon dioxide; energy is provided bysunlight. Nitrogen, phosphorus, and sulfur are also needed in relatively large quantities.Sony VAIO VPCEB1AFX/B Battery

Together, the "Big Six" are the elemental macronutrients for all organisms, often represented by the acronymCHNOPS. Usually they are sourced from inorganic (e.g. carbon dioxide, water, nitrate, phosphate,sulfate) or organic (e.g. carbohydrates, lipids, proteins) compounds, although elemental diatomic molecules of nitrogen and (especially) oxygen are often used.Sony VAIO VPCEB1AGX Battery

Other chemical elements are also necessary to carry out various life processes and build structures; seefertilizer and micronutrient for more information.

Some of these are considered macronutrients in certain organisms. Sony VAIO VPCEB1AGX/BI Battery

The mnemonic C. HOPKiN'S CaFe Mg (to be used as C. Hopkins coffee mug) is used by some students to remember the list as: carbon, hydrogen,oxygen, phosphorus, potassium, nitrogen, sulfur, calcium, iron, and magnesium. Silicon, chloride,sodium, copper, zinc, and molybdenum are sometimes also included, but are in other cases consideredmicronutrients.Sony VAIO VPCEB1BGX Battery

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