Nitrogen (pronounced /ˈnaɪtrədʒɨn/) is a chemical element A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons. Common examples of elements are iron, copper, silver, gold, hydrogen, carbon, that has the symbol N and atomic number The atomic number, Z, should not be confused with the mass number, A, which is the total number of protons and neutrons in the nucleus of an atom. The number of neutrons, N, is known as the neutron number of the atom; thus, A = Z + N. Since protons and neutrons have approximately the same mass , the atomic mass of an atom is roughly equal to A 7 and atomic mass The atomic mass is the mass of an atom, most often expressed in unified atomic mass units. The atomic mass may be considered to be the total mass of protons, neutrons and electrons in a single atom (when the atom is motionless). The atomic mass is sometimes incorrectly used as a synonym of relative atomic mass, average atomic mass and atomic 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert In chemistry, the term inert is used to describe something that is not chemically active. The noble gases were described as being inert because they did not react with the other elements or themselves. It is now understood that the reason that inert gases are completely inert to basic chemical reactions is that their outer valence shell is diatomic Diatomic molecules are molecules composed only of two atoms, of either the same or different chemical elements. The prefix di- means two in Greek. Common diatomic molecules are hydrogen, nitrogen, oxygen, and carbon monoxide. Most elements aside from the noble gases form diatomic molecules when heated, but high temperatures - sometimes thousands gas at standard conditions In physical sciences, standard conditions for temperature and pressure are standard sets of conditions for experimental measurements, to allow comparisons to be made between different sets of data. The most used standards are those of the International Union of Pure and Applied Chemistry (IUPAC) and the National Institute of Standards and, constituting 78% by volume of Earth's atmosphere The Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by the Earth's gravity. It has a mass of about five quadrillion metric tons. Dry air contains roughly (by volume) 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, and trace amounts of other gases. Air also contains a variable amount of water.

Many industrially important compounds, such as ammonia Ammonia is a compound of nitrogen and hydrogen with the formula NH3. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to foodstuffs and fertilizers. Ammonia, either directly or indirectly, is also a building block, nitric acid Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming nitric acid. Fuming nitric acid is characterized as white fuming nitric acid and red fuming nitric acid, depending on the amount of nitrogen dioxide present, organic nitrates (propellants A propellant is a material that is used to move an object. This will often involve a chemical reaction. It may be a gas, liquid, plasma, or, before the chemical reaction, a solid and explosives An explosive material is a material that either is chemically or otherwise energetically unstable or produces a sudden expansion of the material usually accompanied by the production of heat and large changes in pressure upon initiation; this is called the explosion. An explosive charge is a measured quantity of explosive material), and cyanides A cyanide is any chemical compound that contains the cyano group , which consists of a carbon atom triple-bonded to a nitrogen atom. These compounds are usually poisonous. Inorganic cyanides are hydrogen cyanide salts in which cyanide is generally the anion CN-. Organic compounds that have a -C≡N functional group bonded to an alkyl residue are, contain nitrogen. The extremely strong bond in elemental nitrogen dominates nitrogen chemistry, causing difficulty for both organisms and industry in converting the N₂ into useful compounds, and releasing large amounts of energy when these compounds burn or decay back into nitrogen gas.

The element nitrogen was discovered by Daniel Rutherford Daniel Rutherford was a Scottish chemist and physician who is most famous for the isolation of nitrogen in 1772, a Scottish physician, in 1772. Nitrogen occurs in all living organisms. It is a constituent element of amino acids In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent. In the alpha amino acids, the amino and carboxylate groups are attached to and thus of proteins Proteins are organic compounds made of amino acids arranged in a linear chain. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues. The sequence of amino acids in a protein is defined by the sequence of a gene, which is encoded in the genetic code. In, and of nucleic acids A nucleic acid is a macromolecule composed of chains of monomeric nucleotides. In biochemistry these molecules carry genetic information or form structures within cells. The most common nucleic acids are deoxyribonucleic acid and ribonucleic acid (RNA). Nucleic acids are universal in living things, as they are found in all cells and viruses (DNA Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information. DNA is often compared to a set of blueprints or a recipe, or a code, since it contains the instructions needed and RNA Ribonucleic acid is a biologically important type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate. RNA is very similar to DNA, but differs in a few important structural details: in the cell, RNA is usually single-stranded, while DNA is usually double-). It resides in the chemical structure A Chemical structure includes molecular geometry, electronic structure and crystal structure of a chemical compound. Molecular geometry refers to the spatial arrangement of atoms in a molecule and the chemical bonds that hold the atoms together. Molecular geometry can range from the very simple, such as diatomic oxygen or nitrogen molecules, to of almost all neurotransmitters Neurotransmitters are endogenous chemicals which relay, amplify, and modulate signals between a neuron and another cell. Neurotransmitters are packaged into synaptic vesicles that cluster beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to receptors in the membrane on the, and is a defining component of alkaloids Alkaloids are naturally occurring chemical compounds containing basic nitrogen atoms. The name derives from the word alkaline and was used to describe any nitrogen-containing base. Alkaloids are produced by a large variety of organisms, including bacteria, fungi, plants, and animals and are part of the group of natural products . Many alkaloids, biological molecules produced by many organisms.

History

Nitrogen (Latin Latin is an Italic language historically spoken in Latium and Ancient Rome. Through the Roman conquest, Latin spread throughout the Mediterranean and a large part of Europe. Romance languages such as Italian, French, Catalan, Romanian, Spanish, and Portuguese are descended from Latin, while many others, especially European languages, including nitrogenium, where nitrum (from Greek Greek , an Indo-European language native to the southern Balkan peninsula, is the language of the Greeks. It forms an independent branch within Indo-European. It has the longest documented history of any Indo-European language, spanning 34 centuries of written records. In its ancient form, it is the language of classical Ancient Greek literature nitron) means "saltpetre Potassium nitrate is a chemical compound with the chemical formula K " (see nitre Niter or nitre (UK) is the mineral form of potassium nitrate, KNO3, also known as saltpeter (US) or saltpetre (UK). Historically, the term "nitre" – cognate with "natrium", a Latin word for sodium – has been very vaguely defined, and it has been applied to a variety of other minerals and chemical compounds, including sodium), and genes means "forming") is formally considered to have been discovered by Daniel Rutherford Daniel Rutherford was a Scottish chemist and physician who is most famous for the isolation of nitrogen in 1772 in 1772, who called it noxious air or fixed air. That there was a fraction of air that did not support combustion Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering was well known to the late 18th century chemist. Nitrogen was also studied at about the same time by Carl Wilhelm Scheele Carl Wilhelm Scheele was a German-Swedish pharmaceutical chemist. Isaac Asimov called him "hard-luck Scheele" because he made a number of chemical discoveries before others who are generally given the credit. For example, Scheele discovered oxygen (although Joseph Priestley published his findings first), molybdenum and chlorine before, Henry Cavendish Henry Cavendish, FRS was a British scientist noted for his discovery of hydrogen or what he called "inflammable air". He described the density of inflammable air, which formed water on combustion, in a 1766 paper "On Factitious Airs". Antoine Lavoisier later reproduced Cavendish's experiment and gave the element its name, and Joseph Priestley Joseph Priestley (13 March 1733 – 6 February 1804) was an 18th-century British theologian, Dissenting clergyman, natural philosopher, educator, and political theorist who published over 150 works. He is usually credited with the discovery of oxygen, having isolated it in its gaseous state, although Carl Wilhelm Scheele and Antoine Lavoisier also, who referred to it as burnt air or phlogisticated air The phlogiston theory' , first stated in 1667 by Johann Joachim Becher, is a defunct scientific theory that posited the existence of, in addition to the classical four elements of the Greeks, an additional fire-like element called "phlogiston" that was contained within combustible bodies, and released during combustion. The theory was an. Nitrogen gas was inert In chemistry, the term inert is used to describe something that is not chemically active. The noble gases were described as being inert because they did not react with the other elements or themselves. It is now understood that the reason that inert gases are completely inert to basic chemical reactions is that their outer valence shell is enough that Antoine Lavoisier Antoine-Laurent de Lavoisier , the father of modern chemistry, was a French noble prominent in the histories of chemistry and biology. He stated the first version of the law of conservation of mass, recognized and named oxygen (1778) and hydrogen (1783), abolished the phlogiston theory, helped construct the metric system, wrote the first extensive referred to it as "mephetic air" or azote, from the Greek Greek , an Indo-European language native to the southern Balkan peninsula, is the language of the Greeks. It forms an independent branch within Indo-European. It has the longest documented history of any Indo-European language, spanning 34 centuries of written records. In its ancient form, it is the language of classical Ancient Greek literature word άζωτος (azotos) 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. Lavoisier's name for nitrogen is used in French and still remains in English in the common names of many compounds, such as hydrazine and compounds of the azide ion. Compounds of nitrogen were known in the Middle Ages The Middle Ages of European history are a period in history which lasted for roughly a millennium, commonly dated from the fall of the Western Roman Empire in the 5th century to the beginning of the Early Modern Period in the 16th century, marked by the division of Western Christianity in the Reformation, the rise of humanism in the Italian. The alchemists Alchemy (Hebrew:אלכימיה al-himia) is both a philosophy and a practice with an aim of achieving ultimate wisdom as well as immortality, involving the improvement of the alchemist as well as the making of several substances described as possessing unusual properties. The practical aspect of alchemy generated the basics of modern inorganic knew nitric acid Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming nitric acid. Fuming nitric acid is characterized as white fuming nitric acid and red fuming nitric acid, depending on the amount of nitrogen dioxide present as aqua fortis (strong water). The mixture of nitric and hydrochloric acids Hydrochloric acid is the solution of hydrogen chloride (H was known as aqua regia Aqua regia or aqua regis is a highly corrosive, fuming yellow or red solution. The mixture is formed by freshly mixing concentrated nitric acid and concentrated hydrochloric acid, usually in a volumetric ratio of 1:3 respectively. It was so named because it can dissolve the so-called royal, or noble metals gold and platinum, although tantalum, (royal water), celebrated for its ability to dissolve gold Gold is a chemical element with the symbol Au (Latin: aurum) and an atomic number of 79. It has been a highly sought-after precious metal in jewelry, in sculpture, and for ornamentation since the beginning of recorded history. The metal occurs as nuggets or grains in rocks, in veins and in alluvial deposits. Gold is dense, soft, shiny and the most (the king of metals). The earliest military, industrial and agricultural Agriculture refers to the production of food and goods through farming and forestry. Agriculture was the key development that led to the rise of civilization, with the husbandry of domesticated animals and plants creating food surpluses that enabled the development of more densely populated and stratified societies. The study of agriculture is applications of nitrogen compounds involved uses of saltpeter Potassium nitrate is a chemical compound with the chemical formula K (sodium nitrate Sodium nitrate is the chemical compound with the formula NaNO3. This salt, also known as "Chile saltpeter" or "Peru saltpeter" , is a white solid which is very soluble in water. The mineral form is also known as nitratine or soda niter or potassium nitrate Potassium nitrate is a chemical compound with the chemical formula K ), notably in gunpowder Gunpowder, also called black powder, is an explosive mixture of sulfur, charcoal and potassium nitrate, KNO3 that burns rapidly, producing volumes of hot solids and gases which can be used as a propellant in firearms and as a pyrotechnic composition in fireworks. The term gunpowder is also often used more broadly to describe any propellant powder, and much later, as fertilizer Fertilizers are chemical compounds applied to promote plant and fruit growth. Fertilizers are usually applied either through the soil or, by foliar feeding (for uptake through leaves).

Properties

Nitrogen is a nonmetal Nonmetal, or non-metal, is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, every element in the periodic table can be termed either a metal or a nonmetal, with an electronegativity Electronegativity, symbol χ, is a chemical property that describes the ability of an atom to attract electrons (or electron density) towards itself in a covalent bond. An atom's electronegativity is affected by both its atomic weight and the distance that its valence electrons reside from the charged nucleus. The higher the associated of 3.04. It has five electrons The electron is a subatomic particle that carries a negative electric charge. It has no known substructure and is believed to be a point particle. Electrons participate in gravitational, electromagnetic and weak interactions. Like its rest mass and elementary charge, the intrinsic angular momentum of an electron has a constant value. In the in its outer shell An electron shell may be thought of as an orbit followed by electrons around an atom nucleus. Because each shell can contain only a fixed number of electrons, each shell is associated with a particular range of electron energy, and thus each shell must fill completely before electrons can be added to an outer shell. The electrons in the outermost and is therefore trivalent in most compounds. The triple bond in molecular nitrogen (N₂) is the strongest in nature. 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.

At atmospheric pressure molecular nitrogen condenses (liquifies) at 77 K (−195.8 °C) and freezes at 63 K (−210.0 °C) into the beta hexagonal close-packed crystal allotropic form. Below 35.4 K (−237.6 °C) nitrogen assumes the alpha cubic crystal allotropic form. Liquid nitrogen, a fluid resembling water, 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 N₃ and N₄.^[1] 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 diamond, and both have extremely strong covalent bonds. N₄ is nicknamed "nitrogen diamond."^[2]

Isotopes

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. 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, and denitrification) strongly control nitrogen dynamics in the soil. These reactions typically result in ¹⁵N enrichment of the substrate and depletion of the product.

0.73% of the molecular nitrogen in Earth's atmosphere is comprised of the isotopologue ¹⁴N¹⁵N and almost all the rest is ¹⁴N₂.

Radioisotope ¹⁶N is the dominant radionuclide in the coolant of pressurized 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). Because of this, the access to the primary coolant piping must be restricted during reactor power operation^[3]. ¹⁶N is one of the main means used to immediately detect even small leaks from the primary coolant to the secondary steam cycle.

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. 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 as well as in the atmospheres of other planetary bodies. 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).

Reactions

Nitrogen is generally unreactive at standard temperature and pressure. N₂ reacts spontaneously with few reagents, being resilient to acids and bases as well as oxidants and most reductants. When nitrogen reacts spontaneously with a reagent, the net transformation is often called nitrogen fixation.

Nitrogen reacts with elemental lithium at STP.^[4] Lithium burns in an atmosphere of N₂ to give lithium nitride:

6 Li + N₂ → 2 Li₃N

Magnesium also burns in nitrogen, forming magnesium nitride.

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(Ph₂CH₂CH₂PPh₂)₂, and [(η⁵-C₅Me₄H)₂Zr]₂(μ₂,η²,η²-N₂). These complexes illustrate how N₂ might bind to the metal(s) in nitrogenase and the catalyst for the Haber process.^[5] 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.^[4] (see nitrogen fixation)

The starting point for industrial production of nitrogen compounds is the Haber process, in which nitrogen is fixed by reacting N₂ and 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. The reaction, which is the source of the bulk of nitrogen in the biosphere, is catalysed by the nitrogenase enzyme complex which contains Fe and Mo atoms, using energy derived from hydrolysis of adenosine triphosphate (ATP) into adenosine diphosphate and inorganic phosphate (−20.5 kJ/mol).

Occurrence

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 7th most abundant chemical element by mass in the universe.^[6]

Molecular nitrogen and nitrogen compounds have been detected in interstellar space by astronomers using the Far Ultraviolet Spectroscopic Explorer.^[7] Molecular nitrogen is a major constituent of the Saturnian moon Titan's thick atmosphere, and occurs in trace amounts in other planetary atmospheres.^[8]

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 are unable to fix atmospheric nitrogen.

Nitrogen occurs naturally in a number of minerals, such as saltpetre (potassium nitrate), Chile saltpetre (sodium nitrate) and sal ammoniac (ammonium chloride). Most of these are relatively uncommon, partly because of the minerals' ready solubility in water. See also Nitrate minerals and Ammonium minerals.

Compounds

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. In solution ammonia forms the ammonium ion (NH₄⁺). Liquid ammonia (b.p. 240 K) is amphiprotic (displaying either Brønsted-Lowry acidic or basic character) and forms ammonium and the less common amide ions (NH₂^-); 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 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. N₂²⁺ is another polyatomic cation as in hydrazine.

Other classes of nitrogen anions (negatively charged ions) are the poisonous azides (N₃^-), 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. 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. 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 of smog. Nitrogen molecules containing unpaired electrons show an understandable tendency to dimerize (thus pairing the electrons), and are generally highly reactive. The corresponding acids are nitrous HNO₂ and nitric acid HNO₃, with the corresponding salts called nitrites and nitrates.

The higher oxides dinitrogen trioxide N₂O₃, dinitrogen tetroxide N₂O₄ (DTO) and dinitrogen pentoxide N₂O₅, are fairly unstable and explosive, a consequence of the chemical stability of N₂. DTO is one of the most important oxidisers of rocket fuels, used to oxidise hydrazine in the Titan rocket and in the recent NASA MESSENGER probe to Mercury. DTO is an intermediate in the manufacture of nitric acid HNO₃, one of the few acids stronger than hydronium and a fairly strong oxidizing agent.

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. 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.

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.

Applications

Nitrogen gas is an industrial gas produced 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. When supplied compressed in cylinders it is often referred to as OFN (oxygen-free nitrogen).^[9]

Nitrogen gas has a wide variety of applications, including serving as an 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)
• In ordinary incandescent light bulbs as an inexpensive alternative to argon.^[10]
• On top of liquid explosives as a safety measure
• 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^{[citation needed]}
• Use in military aircraft fuel systems to reduce fire hazard, (see inerting system)
• Filling automotive and aircraft tires^[11] due to its inertness and lack of moisture or oxidative qualities, as opposed to air, though this is not necessary for consumer automobiles.^[12][13]

Nitrogen molecules are less likely to escape from the inside of a tire compared with the traditional air mixture used.^{[citation needed]} Air consists mostly of nitrogen and oxygen. Nitrogen molecules have a larger effective diameter than oxygen molecules and therefore diffuse through porous substances more slowly.^[14]

Nitrogen is commonly used during sample preparation procedures for chemical analysis. Specifically, it is used as a means of concentrating and reducing 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.^[15]

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, particularly stouts and British 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.^[16]

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.^{[citation needed]}

Like dry ice, the main use of liquid nitrogen is as a refrigerant.^{[citation needed]} 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 cold traps for certain laboratory equipment and to cool x-ray detectors.^{[citation needed]} It has also been used to cool central processing units and other devices in computers which are overclocked, and which produce more heat than during normal operation.^{[citation needed]}

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 or destroyed. In nature, nitrogen is converted into biologically (and industrially) useful compounds by lightning, 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 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 organic and inorganic salts of nitric acid have been important historically as convenient stores of chemical energy. They include important compounds such as potassium nitrate (or saltpeter used 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 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. When nitrates burn or explode, the formation of the powerful triple bond in the N₂ 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 (N₂O) 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 mimicking the action of nitric oxide.

Biological role

Nitrogen is an essential building block of amino and nucleic acids, essential to life on Earth.

Elemental nitrogen in the atmosphere cannot be used directly by either plants or animals, and must 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.^[17] This was first proposed by Liebig in 1827 and later confirmed.^[17] However, because ammonium is preferentially retained by the forest canopy relative to atmospheric nitrate, most fixed nitrogen that reaches the soil surface under trees as nitrate. Soil nitrate is preferentially assimilated by these tree roots relative to soil ammonium^{[citation needed]}.

Specific bacteria (e.g. Rhizobium trifolium) possess nitrogenase enzymes which 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^{[citation needed]}. Such bacteria may live freely in soil (e.g. Azotobacter) but normally exist in a symbiotic relationship^{[citation needed]} 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, and Gunnera.

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)^{[citation needed]}. In return for the 'fixed' nitrogen, the plant secretes sugars to the symbiotic bacteria^{[citation needed]}.

Some plants^[which?] 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 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. 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.^[18]

Soluble nitrate is an important limiting factor in the growth of certain bacteria in ocean waters^{[citation needed]}. 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^{[citation needed]}. 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. Well-known "dead zone" areas in the U.S. Gulf Coast and the Black Sea are due to this important polluting process^{[citation needed]}.

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 not fresh saltwater fish ^[19]. In animals, free radical nitric oxide (NO) (derived from an amino acid), serves as an important regulatory molecule for circulation^{[citation needed]}.

Animal metabolism of NO results in production of nitrite^{[citation needed]}. 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^{[citation needed]}. The characteristic odor of animal flesh decay is caused by the creation of long-chain, nitrogen-containing amines, such as putrescine and cadaverine^{[citation needed]}.

Decay of organisms and their waste products may produce small amounts of nitrate^{[citation needed]}, but most decay eventually returns nitrogen content to the atmosphere^{[citation needed]}, as molecular nitrogen . The circulation of nitrogen from atmosphere to organic compounds and back is referred to as the nitrogen cycle.

Safety

Rapid release of nitrogen gas into an enclosed space can displace oxygen, and therefore represents an asphyxiation hazard. This may happen with few warning symptoms, since the human carotid body is a relatively slow and a poor low-oxygen (hypoxia) sensing system.^[20] An example occurred shortly before the launch of the first Space Shuttle mission in 1981, when two technicians lost consciousness and 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. 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.^[21][22]

Nitrogen also dissolves in the bloodstream and body fats. 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, nerves, joints, and other sensitive or vital areas.^[23][24] 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.^[25]

Direct skin contact with liquid nitrogen will eventually cause severe frostbite (cryogenic burns). This may happen almost instantly on contact, 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). 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 droplets or pools of undisturbed liquid nitrogen may be prevented for a few seconds by a layer of insulating gas from the Leidenfrost effect. However, liquid nitrogen applied to skin in mists, and on fabrics, bypasses this effect.

See also

• Industrial gas
• Liquid nitrogen
• Nitrogen asphyxiation
• Nitrogenomics
• Nutrient
• Super triphosphate
• Tetranitrogen
• TKN

References

1. ^ "A new molecule and a new signature - Chemistry - tetranitrogen". Science News. February 16, 2002. http://www.findarticles.com/p/articles/mi_m1200/is_7_161/ai_83477565. Retrieved on 2007-08-18.
2. ^ "Polymeric nitrogen synthesized". physorg.com. 2004-08-05. http://www.physorg.com/news693.html. Retrieved on 2009-06-22.
3. ^ Karl Heinz Neeb, "The Radiochemistry of Nuclear Power Plants with Light Water Reactors", Walter de Gruyter, Berlin-New York, 1997.
4. ^ ^{a b} Richard R. Schrock (2005). "Catalytic Reduction of Dinitrogen to Ammonia at a Single Molybdenum Center". Acc. Chem. Res. 38: 955–962. doi:10.1021/ar0501121.
5. ^ Fryzuk, M. D. and Johnson, S. A. (2000). "The continuing story of dinitrogen activation". Coordination Chemistry Reviews 200–202: 379. doi:10.1016/S0010-8545(00)00264-2.
6. ^ Croswell, Ken (February 1996). Alchemy of the Heavens. Anchor. ISBN 0-385-47214-5. http://kencroswell.com/alchemy.html.
7. ^ Daved M. Meyer, Jason A. Cardelli, and Ulysses J. Sofia (1997). "Abundance of Interstellar Nitrogen". arXiv. http://arxiv.org/abs/astro-ph/9710162v1. Retrieved on 2007-12-24.
8. ^ Calvin J. Hamilton. "Titan (Saturn VI)". Solarviews.com. http://www.solarviews.com/eng/titan.htm. Retrieved on 2007-12-24.
9. ^ Reich, Murray; Kapenekas, Harry (1957). "Nitrogen Purfication. Pilot Plant Removal of Oxygen". Industrial & Engineering Chemistry 49: 869. doi:10.1021/ie50569a032.
10. ^ ed. by Charlie Harding ... Royal Society Chemistry; Open University. (2002). Elements of the p Block. Cambridge: Royal Society of Chemistry. ISBN 9780854046904. http://books.google.de/books?id=W0HW8wgmQQsC&pg=PA90.
11. ^ "Why don't they use normal air in race car tires?". Howstuffworks. http://auto.howstuffworks.com/question594.htm. Retrieved on 2006-07-22.
12. ^ "Diffusion, moisture and tyre expansion". Car Talk. http://www.cartalk.com/content/columns/Archive/1997/September/05.html. Retrieved on 2006-07-22.
13. ^ "Is it better to fill your tires with nitrogen instead of air?". The Straight Dope. http://www.straightdope.com/columns/070216.html. Retrieved on 2007-02-16.
14. ^ G. J. Van Amerongen (1946). "The Permeability of Different Rubbers to Gases and Its Relation to Diffusivity and Solubility". Journal of Applied Physics 17 (11): 972–985. doi:10.1063/1.1707667.
15. ^ Kemmochi, Y (2002). "Centrifugal concentrator for the substitution of nitrogen blow-down micro-concentration in dioxin/polychlorinated biphenyl sample preparation". Journal of Chromatography A 943: 295. doi:10.1016/S0021-9673(01)01466-2.
16. ^ Howstuffworks "How does the widget in a beer can work?"
17. ^ ^{a b} Rakov, Vladimir A.; Uman, Martin A. (2007). Lightning: Physics and Effects. Cambridge University Press. p. 508. ISBN 9780521035415.
18. ^ Jahn, GC, LP Almazan, and J Pacia (2005). "Effect of nitrogen fertilizer on the intrinsic rate of increase of the rusty plum aphid, Hysteroneura setariae (Thomas) (Homoptera: Aphididae) on rice (Oryza sativa L.)". Environmental Entomology 34 (4): 938–943. http://puck.esa.catchword.org/vl=33435372/cl=21/nw=1/rpsv/cw/esa/0046225x/v34n4/s26/p938.
19. ^ PMID 15186102
20. ^ "Biology Safety - Cryogenic materials. The risks posed by them". University of Bath. http://www.bath.ac.uk/internal/bio-sci/bbsafe/asphyx.htm. Retrieved on 2007-01-03.
21. ^ Fowler, B; Ackles, KN; Porlier, G (1985). "Effects of inert gas narcosis on behavior--a critical review.". Undersea Biomed. Res. 12 (4): 369–402. ISSN 0093-5387. OCLC 2068005. PMID 4082343. http://archive.rubicon-foundation.org/3019. Retrieved on 2008-09-21.
22. ^ W. H. Rogers; G. Moeller (1989). "Effect of brief, repeated hyperbaric exposures on susceptibility to nitrogen narcosis". Undersea Biomed. Res. 16 (3): 227–32. ISSN 0093-5387. OCLC 2068005. PMID 2741255. http://archive.rubicon-foundation.org/2522. Retrieved on 2008-09-21.
23. ^ Acott, C. (1999). "A brief history of diving and decompression illness.". South Pacific Underwater Medicine Society journal 29 (2). ISSN 0813-1988. OCLC 16986801. http://archive.rubicon-foundation.org/6004. Retrieved on 2008-09-21.
24. ^ Kindwall, E. P.; A. Baz; E. N. Lightfoot; E. H. Lanphier; A. Seireg. (1975). "Nitrogen elimination in man during decompression.". Undersea Biomed. Res. 2 (4): 285–97. ISSN 0093-5387. OCLC 2068005. PMID 1226586. http://archive.rubicon-foundation.org/2741. Retrieved on 2008-09-21.
25. ^ US Navy Diving Manual, 6th revision. United States: US Naval Sea Systems Command. 2006. http://www.supsalv.org/00c3_publications.asp?destPage=00c3&pageID=3.9. Retrieved on 2008-04-24.

Further reading

• Garrett, Reginald H.; Grisham, Charles M. (1999). Biochemistry (2nd ed.). Fort Worth: Saunders College Publ.. ISBN 0030223180.

• Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. ISBN 0080220576.

• "Nitrogen". Los Alamos National Laboratory. 2003-10-20. http://periodic.lanl.gov/elements/7.html.

External links

• Etymology of Nitrogen
• Why high nitrogen density in explosives?
• WebElements.com – Nitrogen
• It's Elemental – Nitrogen
• Schenectady County Community College – Nitrogen
• Nitrogen N2 Properties, Uses, Applications
• Handling procedures for liquid nitrogen
• Material Safety Data Sheet

Categories: Nitrogen | Chemical elements | Coolants | Dielectrics | Laser gain media | Biology and pharmacology of chemical elements

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• Nitrogen

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