mephitic air" or ''azote'', from the
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
word (azotikos), "no life", due to it being
asphyxiant
An asphyxiant gas, also known as a simple asphyxiant, is a nontoxic or minimally toxic gas which reduces or displaces the normal oxygen concentration in breathing air. Breathing of oxygen-depleted air can lead to death by asphyxiation (suffocation) ...
. In an atmosphere of pure nitrogen, animals died and flames were extinguished. Though Lavoisier's name was not accepted in English since it was pointed out that all gases but oxygen are either asphyxiant or outright toxic, it is used in many languages (French, Italian, Portuguese, Polish, Russian, Albanian, Turkish, etc.; the German ''Stickstoff'' similarly refers to the same characteristic, viz. ''ersticken'' "to choke or suffocate") and still remains in English in the common names of many nitrogen compounds, such as
hydrazine and compounds of the
azide ion. Finally, it led to the name "
pnictogen
A pnictogen ( or ; from grc, πνῑ́γω "to choke" and -gen, "generator") is any of the chemical elements in group 15 of the periodic table. Group 15 is also known as the nitrogen group or nitrogen family. Group 15 consists of the el ...
s" for the group headed by nitrogen, from the Greek πνίγειν "to choke".
[Greenwood and Earnshaw, pp. 406–07]
The English word nitrogen (1794) entered the language from the French ''nitrogène'', coined in 1790 by French chemist
Jean-Antoine Chaptal
Jean-Antoine Chaptal, comte de Chanteloup (5 June 1756 – 30 July 1832) was a French chemist, physician, agronomist, industrialist, statesman, educator and philanthropist. His multifaceted career unfolded during one of the most brilliant periods ...
(1756–1832), from the French ''nitre'' (
potassium nitrate
Potassium nitrate is a chemical compound with the chemical formula . This alkali metal nitrate salt is also known as Indian saltpetre (large deposits of which were historically mined in India). It is an ionic salt of potassium ions K+ and nitr ...
, also called
saltpeter
Potassium nitrate is a chemical compound with the chemical formula . This alkali metal nitrate Salt (chemistry), salt is also known as Indian saltpetre (large deposits of which were historically mined in India). It is an ionic salt of potassium ...
) and the French suffix ''-gène'', "producing", from the
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
-γενής (-genes, "begotten"). Chaptal's meaning was that nitrogen is the essential part of
nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...
, which in turn was produced from
nitre
Niter or nitre is the mineral form of potassium nitrate, KNO3. It is a soft, white, highly soluble mineral found primarily in arid climates or cave deposits.
Historically, the term ''niter'' was not well differentiated from natron, both of w ...
. In earlier times, niter had been confused with Egyptian "natron" (
sodium carbonate) – called νίτρον (nitron) in Greek – which, despite the name, contained no nitrate.
The earliest military, industrial, and agricultural applications of nitrogen compounds used saltpeter (
sodium nitrate or potassium nitrate), most notably in
gunpowder
Gunpowder, also commonly known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur, carbon (in the form of charcoal) and potassium nitrate (saltpeter). Th ...
, and later as
fertiliser
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
. In 1910,
Lord Rayleigh
John William Strutt, 3rd Baron Rayleigh, (; 12 November 1842 – 30 June 1919) was an English mathematician and physicist who made extensive contributions to science. He spent all of his academic career at the University of Cambridge. Am ...
discovered that an electrical discharge in nitrogen gas produced "active nitrogen", a
monatomic
In physics and chemistry, "monatomic" is a combination of the words "mono" and "atomic", and means "single atom". It is usually applied to gases: a monatomic gas is a gas in which atoms are not bound to each other. Examples at standard conditions ...
allotrope of nitrogen. The "whirling cloud of brilliant yellow light" produced by his apparatus reacted with
mercury to produce explosive
mercury nitride.
For a long time, sources of nitrogen compounds were limited. Natural sources originated either from biology or deposits of nitrates produced by atmospheric reactions.
Nitrogen fixation
Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...
by industrial processes like the
Frank–Caro process (1895–1899) and
Haber–Bosch process
The Haber process, also called the Haber–Bosch process, is an artificial nitrogen fixation process and is the main industrial procedure for the production of ammonia today. It is named after its inventors, the German chemists Fritz Haber and C ...
(1908–1913) eased this shortage of nitrogen compounds, to the extent that half of global
food production
The food industry is a complex, global network of diverse businesses that supplies most of the food consumed by the world's population. The food industry today has become highly diversified, with manufacturing ranging from small, traditiona ...
(see Applications) now relies on synthetic nitrogen fertilisers.
At the same time, use of the
Ostwald process The Ostwald process is a chemical process used for making nitric acid (HNO3). Wilhelm Ostwald developed the process, and he patented it in 1902. The Ostwald process is a mainstay of the modern chemical industry, and it provides the main raw materi ...
(1902) to produce nitrates from industrial nitrogen fixation allowed the large-scale industrial production of nitrates as
feedstock in the manufacture of
explosives in the
World Wars
A world war is an international conflict which involves all or most of the world's major powers. Conventionally, the term is reserved for two major international conflicts that occurred during the first half of the 20th century, World WarI (1914 ...
of the 20th century.
Properties
Atomic
![Neon orbitals](https://upload.wikimedia.org/wikipedia/commons/5/58/Neon_orbitals.png)
A nitrogen atom has seven electrons. In the ground state, they are arranged in the electron configuration 1s2s2p2p2p. It, therefore, has five
valence electron
In chemistry and physics, a valence electron is an electron in the outer shell associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed. In a single covalent bond, a shared pair form ...
s in the 2s and 2p orbitals, three of which (the p-electrons) are unpaired. It has one of the highest
electronegativities
Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the d ...
among the elements (3.04 on the Pauling scale), exceeded only by
chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
(3.16),
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
(3.44), and
fluorine (3.98). (The light
noble gas
The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low ch ...
es,
helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
,
neon, and
argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as ...
, would presumably also be more electronegative, and in fact are on the Allen scale.)
Following periodic trends, its single-bond
covalent radius
The covalent radius, ''r''cov, is a measure of the size of an atom that forms part of one covalent bond. It is usually measured either in picometres (pm) or angstroms (Å), with 1 Å = 100 pm.
In principle, the sum of the two coval ...
of 71 pm is smaller than those of
boron (84 pm) and
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...
(76 pm), while it is larger than those of oxygen (66 pm) and fluorine (57 pm). The
nitride
In chemistry, a nitride is an inorganic compound of nitrogen. The "nitride" anion, N3- ion, is very elusive but compounds of nitride are numerous, although rarely naturally occuring. Some nitrides have a find applications, such as wear-resistant ...
anion, N
3−, is much larger at 146 pm, similar to that of the
oxide (O
2−: 140 pm) and
fluoride (F
−: 133 pm) anions.
The first three ionisation energies of nitrogen are 1.402, 2.856, and 4.577 MJ·mol
−1, and the sum of the fourth and fifth is . Due to these very high figures, nitrogen has no simple cationic chemistry.
[Greenwood and Earnshaw, p. 550]
The lack of radial nodes in the 2p subshell is directly responsible for many of the anomalous properties of the first row of the
p-block
A block of the periodic table is a set of elements unified by the atomic orbitals their valence electrons or vacancies lie in. The term appears to have been first used by Charles Janet. Each block is named after its characteristic orbital: s-blo ...
, especially in nitrogen, oxygen, and fluorine. The 2p subshell is very small and has a very similar radius to the 2s shell, facilitating
orbital hybridisation. It also results in very large electrostatic forces of attraction between the nucleus and the valence electrons in the 2s and 2p shells, resulting in very high electronegativities.
Hypervalency
In chemistry, a hypervalent molecule (the phenomenon is sometimes colloquially known as expanded octet) is a molecule that contains one or more main group elements apparently bearing more than eight electrons in their valence shells. Phosphorus ...
is almost unknown in the 2p elements for the same reason, because the high electronegativity makes it difficult for a small nitrogen atom to be a central atom in an electron-rich
three-center four-electron bond
The 3-center 4-electron (3c–4e) bond is a model used to explain bonding in certain hypervalent molecules such as tetratomic and hexatomic interhalogen compounds, sulfur tetrafluoride, the xenon fluorides, and the bifluoride ion. It is also know ...
since it would tend to attract the electrons strongly to itself. Thus, despite nitrogen's position at the head of group 15 in the periodic table, its chemistry shows huge differences from that of its heavier congeners
phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
,
arsenic
Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, ...
,
antimony
Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient t ...
, and
bismuth
Bismuth is a chemical element with the symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental bismuth occurs ...
.
Nitrogen may be usefully compared to its horizontal neighbours' carbon and oxygen as well as its vertical neighbours in the pnictogen column, phosphorus, arsenic, antimony, and bismuth. Although each period 2 element from lithium to oxygen shows some similarities to the period 3 element in the next group (from magnesium to chlorine; these are known as
diagonal relationship
A diagonal relationship is said to exist between certain pairs of diagonally adjacent elements in the second and third periods (first 20 elements) of the periodic table. These pairs (lithium (Li) and magnesium (Mg), beryllium (Be) and aluminium ...
s), their degree drops off abruptly past the boron–silicon pair. The similarities of nitrogen to sulfur are mostly limited to sulfur nitride ring compounds when both elements are the only ones present.
Nitrogen does not share the proclivity of carbon for
catenation. Like carbon, nitrogen tends to form ionic or metallic compounds with metals. Nitrogen forms an extensive series of nitrides with carbon, including those with chain-,
graphitic-, and
fullerenic-like structures.
It resembles oxygen with its high electronegativity and concomitant capability for
hydrogen bonding and the ability to form
coordination complex
A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as '' ligands'' or complexing agents. ...
es by donating its
lone pairs of electrons. There are some parallels between the chemistry of ammonia NH
3 and water H
2O. For example, the capacity of both compounds to be protonated to give NH
4+ and H
3O
+ or deprotonated to give NH
2− and OH
−, with all of these able to be isolated in solid compounds.
Nitrogen shares with both its horizontal neighbours a preference for forming multiple bonds, typically with carbon, oxygen, or other nitrogen atoms, through p
''π''–p
''π'' interactions.
Thus, for example, nitrogen occurs as diatomic molecules and therefore has very much lower
melting
Melting, or fusion, is a physical process that results in the phase transition of a substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the application of heat or pressure, which inc ...
(−210 °C) and
boiling points (−196 °C) than the rest of its group, as the N
2 molecules are only held together by weak
van der Waals interaction
In molecular physics, the van der Waals force is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; they are comparatively weak and the ...
s and there are very few electrons available to create significant instantaneous dipoles. This is not possible for its vertical neighbours; thus, the
nitrogen oxides,
nitrites,
nitrates,
nitro-,
nitroso
In organic chemistry, nitroso refers to a functional group in which the nitric oxide () group is attached to an organic moiety (chemistry), moiety. As such, various nitroso groups can be categorized as ''C''-nitroso compounds (e.g., nitrosoalkane ...
-,
azo-, and
diazo-compounds,
azides,
cyanate
Cyanate is an anion with the structural formula , usually written . It also refers to any salt containing it, such as ammonium cyanate.
It is an isomer of the much less stable fulminate anion .William R. Martin and David W. Ball (2019): "Sma ...
s,
thiocyanate
Thiocyanate (also known as rhodanide) is the anion . It is the conjugate base of thiocyanic acid. Common derivatives include the colourless salts potassium thiocyanate and sodium thiocyanate. Mercury(II) thiocyanate was formerly used in pyr ...
s, and
imino
In organic chemistry, an imine ( or ) is a functional group or organic compound containing a carbon–nitrogen double bond (). The nitrogen atom can be attached to a hydrogen or an organic group (R). The carbon atom has two additional single bon ...
-derivatives find no echo with phosphorus, arsenic, antimony, or bismuth. By the same token, however, the complexity of the phosphorus oxoacids finds no echo with nitrogen.
Setting aside their differences, nitrogen and phosphorus form an extensive series of compounds with one another; these have chain, ring, and cage structures.
Table of thermal and physical properties of nitrogen (N2) at atmospheric pressure:
Isotopes
![NuclideMap C-F](https://upload.wikimedia.org/wikipedia/commons/c/c8/NuclideMap_C-F.png)
Nitrogen has two stable
isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numb ...
s:
14N and
15N. The first is much more common, making up 99.634% of natural nitrogen, and the second (which is slightly heavier) makes up the remaining 0.366%. This leads to an atomic weight of around 14.007 u.
[Greenwood and Earnshaw, pp. 411–12] Both of these stable isotopes are produced in the
CNO cycle
The CNO cycle (for carbon–nitrogen–oxygen; sometimes called Bethe–Weizsäcker cycle after Hans Albrecht Bethe and Carl Friedrich von Weizsäcker) is one of the two known sets of fusion reactions by which stars convert hydrogen to helium, ...
in
stars, but
14N is more common as its neutron capture is the rate-limiting step.
14N is one of the five stable
odd–odd nuclides (a nuclide having an odd number of protons and neutrons); the other four are
2H,
6Li,
10B, and
180mTa.
The relative abundance of
14N and
15N is practically constant in the atmosphere but can vary elsewhere, due to natural isotopic fractionation from biological
redox
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
reactions and the evaporation of natural
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
or
nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...
. Biologically mediated reactions (e.g.,
assimilation,
nitrification
''Nitrification'' is the biological oxidation of ammonia to nitrite followed by the oxidation of the nitrite to nitrate occurring through separate organisms or direct ammonia oxidation to nitrate in comammox bacteria. The transformation of am ...
, and
denitrification
Denitrification is a microbially facilitated process where nitrate (NO3−) is reduced and ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products. Facultative anaerobic bacteria perform denitr ...
) strongly control nitrogen dynamics in the soil. These reactions typically result in
15N enrichment of the
substrate and depletion of the
product
Product may refer to:
Business
* Product (business), an item that serves as a solution to a specific consumer problem.
* Product (project management), a deliverable or set of deliverables that contribute to a business solution
Mathematics
* Produ ...
.
The heavy isotope
15N was first discovered by S. M. Naudé in 1929, and soon after heavy isotopes of the neighbouring elements
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
and
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...
were discovered.
[Greenwood and Earnshaw, p. 408] It presents one of the lowest thermal neutron capture cross-sections of all isotopes. It is frequently used in
nuclear magnetic resonance
Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a strong constant magnetic field are perturbed by a weak oscillating magnetic field (in the near field) and respond by producing an electromagnetic signal with a ...
(NMR) spectroscopy to determine the structures of nitrogen-containing molecules, due to its fractional
nuclear spin of one-half, which offers advantages for NMR such as narrower line width.
14N, though also theoretically usable, has an integer nuclear spin of one and thus has a
quadrupole moment
A quadrupole or quadrapole is one of a sequence of configurations of things like electric charge or current, or gravitational mass that can exist in ideal form, but it is usually just part of a multipole expansion of a more complex structure ref ...
that leads to wider and less useful spectra.
15N NMR nevertheless has complications not encountered in the more common
1H and
13C NMR spectroscopy. The low natural abundance of
15N (0.36%) significantly reduces sensitivity, a problem which is only exacerbated by its low
gyromagnetic ratio, (only 10.14% that of
1H). As a result, the signal-to-noise ratio for
1H is about 300 times as much as that for
15N at the same magnetic field strength.
This may be somewhat alleviated by isotopic enrichment of
15N by chemical exchange or fractional distillation.
15N-enriched compounds have the advantage that under standard conditions, they do not undergo chemical exchange of their nitrogen atoms with atmospheric nitrogen, unlike compounds with labelled
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
, carbon, and oxygen isotopes that must be kept away from the atmosphere.
The
15N:
14N ratio is commonly used in stable isotope analysis in the fields of
geochemistry
Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the ...
,
hydrology
Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and environmental watershed sustainability. A practitioner of hydrology is call ...
,
paleoclimatology
Paleoclimatology (American and British English spelling differences, British spelling, palaeoclimatology) is the study of climates for which direct measurements were not taken. As instrumental records only span a tiny part of Earth's history, the ...
and
paleoceanography
Paleoceanography is the study of the history of the oceans in the geologic past with regard to circulation, chemistry, biology, geology and patterns of sedimentation and biological productivity. Paleoceanographic studies using environment models ...
, where it is called
''δ''15N.
Of the ten other isotopes produced synthetically, ranging from
12N to
23N,
13N has a
half-life
Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable at ...
of ten minutes and the remaining isotopes have half-lives on the order of seconds (
16N and
17N) or milliseconds. No other nitrogen isotopes are possible as they would fall outside the
nuclear drip line
The nuclear drip line is the boundary beyond which atomic nuclei decay by the emission of a proton or neutron.
An arbitrary combination of protons and neutrons does not necessarily yield a stable nucleus. One can think of moving up and/or to ...
s, leaking out a proton or neutron.
Given the half-life difference,
13N is the most important nitrogen radioisotope, being relatively long-lived enough to use in
positron emission tomography (PET), although its half-life is still short and thus it must be produced at the venue of the PET, for example in a
cyclotron
A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: Jan ...
via proton bombardment of
16O producing
13N and an
alpha particle
Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be pr ...
.
The
radioisotope
A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferr ...
16N is the dominant
radionuclide in the coolant of
pressurised water reactor
A pressurized water reactor (PWR) is a type of light-water nuclear reactor. PWRs constitute the large majority of the world's nuclear power plants (with notable exceptions being the UK, Japan and Canada). In a PWR, the primary coolant (water) is ...
s or
boiling water reactor
A boiling water reactor (BWR) is a type of light water nuclear reactor used for the generation of electrical power. It is a design different from a Soviet graphite-moderated RBMK. It is the second most common type of electricity-generating nu ...
s during normal operation. It is produced from
16O (in water) via an
(n,p) reaction, in which the
16O atom captures a neutron and expels a proton. 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, access to the primary coolant piping in a pressurised water reactor must be restricted during
reactor power operation.
It is a sensitive and immediate indicator of leaks from the primary coolant system to the secondary steam cycle and is the primary means of detection for such leaks.
Chemistry and compounds
Allotropes
![N2MolecularDiagramCR](https://upload.wikimedia.org/wikipedia/commons/4/41/N2MolecularDiagramCR.jpg)
Atomic nitrogen, also known as active nitrogen, is highly reactive, being a
triradical with three unpaired electrons. Free nitrogen atoms easily react with most elements to form nitrides, and even when two free nitrogen atoms collide to produce an excited N
2 molecule, they may release so much energy on collision with even such stable molecules as
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
and
water
Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
to cause homolytic fission into radicals such as CO and O or OH and H. Atomic nitrogen is prepared by passing an electric discharge through nitrogen gas at 0.1–2 mmHg, which produces atomic nitrogen along with a peach-yellow emission that fades slowly as an afterglow for several minutes even after the discharge terminates.
[Greenwood and Earnshaw, pp. 412–16]
Given the great reactivity of atomic nitrogen, elemental nitrogen usually occurs as molecular N
2, dinitrogen. This molecule is a colourless, odourless, and tasteless
diamagnetic
Diamagnetic materials are repelled by a magnetic field; an applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force. In contrast, paramagnetic and ferromagnetic materials are attracted ...
gas at standard conditions: it melts at −210 °C and boils at −196 °C.
Dinitrogen is mostly unreactive at room temperature, but it will nevertheless react with
lithium
Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid ...
metal and some
transition metal
In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that ca ...
complexes. This is due to its bonding, which is unique among the diatomic elements at standard conditions in that it has an N≡N
triple bond
A triple bond in chemistry is a chemical bond between two atoms involving six bonding electrons instead of the usual two in a covalent single bond. Triple bonds are stronger than the equivalent single bonds or double bonds, with a bond order o ...
. Triple bonds have short bond lengths (in this case, 109.76 pm) and high dissociation energies (in this case, 945.41 kJ/mol), and are thus very strong, explaining dinitrogen's low level of chemical reactivity.
Other nitrogen
oligomers
In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relativ ...
and polymers may be possible. If they could be synthesised, they may have potential applications as materials with a very high energy density, that could be used as powerful propellants or explosives.
Under extremely high pressures (1.1 million
atm) and high temperatures (2000 K), as produced in a
diamond anvil cell
A diamond anvil cell (DAC) is a high-pressure device used in geology, engineering, and materials science experiments. It enables the compression of a small (sub-millimeter-sized) piece of material to extreme pressures, typically up to around 1 ...
, nitrogen polymerises into the single-bonded
cubic gauche
Cubic may refer to:
Science and mathematics
* Cube (algebra), "cubic" measurement
* Cube, a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex
** Cubic crystal system, a crystal system w ...
crystal structure. This structure is similar to that of
diamond
Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure, ...
, and both have extremely strong
covalent bonds, resulting in its nickname "nitrogen diamond".
![Mountainous Shoreline of Sputnik Planum (PIA20198)](https://upload.wikimedia.org/wikipedia/commons/6/67/Mountainous_Shoreline_of_Sputnik_Planum_%28PIA20198%29.png)
At
atmospheric pressure
Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, ...
, molecular nitrogen
condenses
Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor to ...
(
liquefies) at 77
K (−195.79 °
C) and
freezes
Freezing is a phase transition where a liquid turns into a solid when its temperature is lowered below its freezing point. In accordance with the internationally established definition, freezing means the solidification phase change of a liquid o ...
at 63 K (−210.01 °C)
into the beta
hexagonal close-packed
In geometry, close-packing of equal spheres is a dense arrangement of congruent spheres in an infinite, regular arrangement (or lattice). Carl Friedrich Gauss proved that the highest average density – that is, the greatest fraction of space occu ...
crystal
allotropic
Allotropy or allotropism () is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements. Allotropes are different structural modifications of an element: th ...
form. Below 35.4 K (−237.6 °C) nitrogen assumes the
cubic crystal allotropic form (called the alpha phase).
Liquid nitrogen, a colourless 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
In physics, cryogenics is the production and behaviour of materials at very low temperatures.
The 13th IIR International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of “cryogenics” and “cr ...
.
Solid nitrogen
Solid nitrogen is a number of solid forms of the element nitrogen, first observed in 1884. Solid nitrogen is mainly the subject of academic research, but low-temperature, low-pressure solid nitrogen is a substantial component of bodies in the ou ...
has many crystalline modifications. It forms a significant dynamic surface coverage on Pluto and outer moons of the Solar System such as
Triton
Triton commonly refers to:
* Triton (mythology), a Greek god
* Triton (moon), a satellite of Neptune
Triton may also refer to:
Biology
* Triton cockatoo, a parrot
* Triton (gastropod), a group of sea snails
* ''Triton'', a synonym of ''Triturus' ...
. Even at the low temperatures of solid nitrogen it is fairly volatile and can
sublime to form an atmosphere, or condense back into nitrogen frost. It is very weak and flows in the form of glaciers and on Triton
geysers of nitrogen gas come from the polar ice cap region.
Dinitrogen complexes
![RuA5N2](https://upload.wikimedia.org/wikipedia/commons/5/5b/RuA5N2.png)
The first example of a
dinitrogen complex
Transition metal dinitrogen complexes are coordination compounds that contain transition metals as ion centers the dinitrogen molecules (N2) as ligands.
Historical background
Transition metal complexes of N2 have been studied since 1965 when ...
to be discovered was
3)5(N2)">u(NH3)5(N2)sup>2+ (see figure at right), and soon many other such complexes were discovered. These
complexes, in which a nitrogen molecule donates at least one lone pair of electrons to a central metal cation, illustrate how N
2 might bind to the metal(s) in
nitrogenase
Nitrogenases are enzymes () that are produced by certain bacteria, such as cyanobacteria (blue-green bacteria) and rhizobacteria. These enzymes are responsible for the reduction of nitrogen (N2) to ammonia (NH3). Nitrogenases are the only fa ...
and the
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
for the
Haber process
The Haber process, also called the Haber–Bosch process, is an artificial nitrogen fixation process and is the main industrial procedure for the production of ammonia today. It is named after its inventors, the German chemists Fritz Haber and ...
: these processes involving dinitrogen activation are vitally important in biology and in the production of fertilisers.
Dinitrogen is able to coordinate to metals in five different ways. The more well-characterised ways are the end-on M←N≡N (''
η''
1) and M←N≡N→M (''bridging ligand, μ'', bis-''η''
1), in which the lone pairs on the nitrogen atoms are donated to the metal cation. The less well-characterised ways involve dinitrogen donating electron pairs from the triple bond, either as a bridging ligand to two metal cations (''μ'', bis-''η''
2) or to just one (''η''
2). The fifth and unique method involves triple-coordination as a bridging ligand, donating all three electron pairs from the triple bond (''μ''
3-N
2). A few complexes feature multiple N
2 ligands and some feature N
2 bonded in multiple ways. Since N
2 is isoelectronic with
carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
(CO) and acetylene (C
2H
2), the bonding in dinitrogen complexes is closely allied to that in carbonyl compounds, although N
2 is a weaker ''σ''-donor and ''π''-acceptor than CO. Theoretical studies show that ''σ'' donation is a more important factor allowing the formation of the M–N bond than ''π'' back-donation, which mostly only weakens the N–N bond, and end-on (''η''
1) donation is more readily accomplished than side-on (''η''
2) donation.
Today, dinitrogen complexes are known for almost all the
transition metal
In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that ca ...
s, accounting for several hundred compounds. They are normally prepared by three methods:
# Replacing labile ligands such as water, H
2O, hydride, H
−, or carbon monoxide, CO directly by nitrogen: these are often reversible reactions that proceed at mild conditions.
# Reducing metal complexes in the presence of a suitable co-ligand in excess under nitrogen gas. A common choice includes replacing chloride ligands with dimethylphenylphosphine (PMe
2Ph) to make up for the smaller number of nitrogen ligands attached to the original chlorine ligands.
# Converting a ligand with N–N bonds, such as hydrazine or azide, directly into a dinitrogen ligand.
Occasionally the N≡N bond may be formed directly within a metal complex, for example by directly reacting coordinated
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
(NH
3) with nitrous acid (HNO
2), but this is not generally applicable. Most dinitrogen complexes have colours within the range white-yellow-orange-red-brown; a few exceptions are known, such as the blue [
2-(N
2)].
Nitrides, azides, and nitrido complexes
Nitrogen bonds to almost all the elements in the periodic table except the first three
noble gas
The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low ch ...
es,
helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
,
neon, and
argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as ...
, and some of the very short-lived elements after
bismuth
Bismuth is a chemical element with the symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental bismuth occurs ...
, creating an immense variety of binary compounds with varying properties and applications in which pentazenium tetraazidoborate has the highest nitrogen content.
Many binary compounds are known: with the exception of the nitrogen hydrides, oxides, and fluorides, these are typically called
nitride
In chemistry, a nitride is an inorganic compound of nitrogen. The "nitride" anion, N3- ion, is very elusive but compounds of nitride are numerous, although rarely naturally occuring. Some nitrides have a find applications, such as wear-resistant ...
s. Many stoichiometric phases are usually present for most elements (e.g. MnN, Mn
6N
5, Mn
3N
2, Mn
2N, Mn
4N, and Mn
''x''N for 9.2 < ''x'' < 25.3). They may be classified as "salt-like" (mostly ionic), covalent, "diamond-like", and metallic (or interstitial compound, interstitial), although this classification has limitations generally stemming from the continuity of bonding types instead of the discrete and separate types that it implies. They are normally prepared by directly reacting a metal with nitrogen or ammonia (sometimes after heating), or by thermal decomposition of metal amides:
[Greenwood and Earnshaw, pp. 417–20]
:3 Ca + N
2 → Ca
3N
2
:3 Mg + 2 NH
3 → Mg
3N
2 + 3 H
2 (at 900 °C)
:3 Zn(NH
2)
2 → Zn
3N
2 + 4 NH
3
Many variants on these processes are possible. The most ionic of these nitrides are those of the alkali metals and alkaline earth metals, Li
3N (Na, K, Rb, and Cs do not form stable nitrides for steric reasons) and M
3N
2 (M = Be, Mg, Ca, Sr, Ba). These can formally be thought of as salts of the N
3− anion, although charge separation is not actually complete even for these highly electropositive elements. However, the alkali metal
azides NaN
3 and KN
3, featuring the linear anion, are well-known, as are Sr(N
3)
2 and Ba(N
3)
2. Azides of the B-subgroup metals (those in group 11 element, groups 11 through chalcogen, 16) are much less ionic, have more complicated structures, and detonate readily when shocked.
![Borazin Mesomers](https://upload.wikimedia.org/wikipedia/commons/c/cd/Borazin_Mesomers.png)
Many covalent binary nitrides are known. Examples include cyanogen ((CN)
2), triphosphorus pentanitride (P
3N
5), disulfur dinitride (S
2N
2), and tetrasulfur tetranitride (S
4N
4). The essentially covalent silicon nitride (Si
3N
4) and germanium nitride (Ge
3N
4) are also known: silicon nitride, in particular, would make a promising ceramic if not for the difficulty of working with and sintering it. In particular, the boron group, group 13 nitrides, most of which are promising semiconductors, are isoelectronic with graphite, diamond, and silicon carbide and have similar structures: their bonding changes from covalent to partially ionic to metallic as the group is descended. In particular, since the B–N unit is isoelectronic to C–C, and carbon is essentially intermediate in size between boron and nitrogen, much of organic chemistry finds an echo in boron–nitrogen chemistry, such as in borazine ("inorganic benzene"). Nevertheless, the analogy is not exact due to the ease of nucleophile, nucleophilic attack at boron due to its deficiency in electrons, which is not possible in a wholly carbon-containing ring.
The largest category of nitrides are the interstitial nitrides of formulae MN, M
2N, and M
4N (although variable composition is perfectly possible), where the small nitrogen atoms are positioned in the gaps in a metallic cubic or
hexagonal close-packed
In geometry, close-packing of equal spheres is a dense arrangement of congruent spheres in an infinite, regular arrangement (or lattice). Carl Friedrich Gauss proved that the highest average density – that is, the greatest fraction of space occu ...
lattice. They are opaque, very hard, and chemically inert, melting only at very high temperatures (generally over 2500 °C). They have a metallic lustre and conduct electricity as do metals. They hydrolyse only very slowly to give ammonia or nitrogen.
The nitride anion (N
3−) is the strongest ''π'' donor known among ligands (the second-strongest is O
2−). Nitrido complexes are generally made by the thermal decomposition of azides or by deprotonating ammonia, and they usually involve a terminal
3− group. The linear azide anion (), being isoelectronic with nitrous oxide,
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
, and
cyanate
Cyanate is an anion with the structural formula , usually written . It also refers to any salt containing it, such as ammonium cyanate.
It is an isomer of the much less stable fulminate anion .William R. Martin and David W. Ball (2019): "Sma ...
, forms many coordination complexes. Further catenation is rare, although (isoelectronic with carbonate and
nitrate) is known.
Hydrides
![Nitrogen electrode potentials](https://upload.wikimedia.org/wikipedia/commons/6/62/Nitrogen_electrode_potentials.svg)
Industrially,
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
(NH
3) is the most important compound of nitrogen and is prepared in larger amounts than any other compound because it contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilisers. It is a colourless alkaline gas with a characteristic pungent smell. The presence of hydrogen bonding has very significant effects on ammonia, conferring on it its high melting (−78 °C) and boiling (−33 °C) points. As a liquid, it is a very good solvent with a high heat of vaporisation (enabling it to be used in vacuum flasks), that also has a low viscosity and electrical conductivity and high dielectric constant, and is less dense than water. However, the hydrogen bonding in NH
3 is weaker than that in H
2O due to the lower electronegativity of nitrogen compared to oxygen and the presence of only one lone pair in NH
3 rather than two in H
2O. It is a weak base in aqueous solution (acid dissociation constant, p''K''
''b'' 4.74); its conjugate acid is
ammonium, . It can also act as an extremely weak acid, losing a proton to produce the amide anion, . It thus undergoes self-dissociation, similar to water, to produce ammonium and amide. Ammonia burns in air or oxygen, though not readily, to produce nitrogen gas; it burns in fluorine with a greenish-yellow flame to give nitrogen trifluoride. Reactions with the other nonmetals are very complex and tend to lead to a mixture of products. Ammonia reacts on heating with metals to give nitrides.
[Greenwood and Earnshaw, pp. 420–26]
Many other binary nitrogen hydrides are known, but the most important are
hydrazine (N
2H
4) and hydrogen azide (HN
3). Although it is not a nitrogen hydride, hydroxylamine (NH
2OH) is similar in properties and structure to ammonia and hydrazine as well. Hydrazine is a fuming, colourless liquid that smells similar to ammonia. Its physical properties are very similar to those of water (melting point 2.0 °C, boiling point 113.5 °C, density 1.00 g/cm
3). Despite it being an endothermic compound, it is kinetically stable. It burns quickly and completely in air very exothermically to give nitrogen and water vapour. It is a very useful and versatile reducing agent and is a weaker base than ammonia.
It is also commonly used as a rocket fuel.
Hydrazine is generally made by reaction of ammonia with alkaline sodium hypochlorite in the presence of gelatin or glue:
[Greenwood and Earnshaw, pp. 426–33]
:NH
3 + OCl
− → NH
2Cl + OH
−
:NH
2Cl + NH
3 → + Cl
− (slow)
: + OH
− → N
2H
4 + H
2O (fast)
(The attacks by hydroxide and ammonia may be reversed, thus passing through the intermediate NHCl
− instead.) The reason for adding gelatin is that it removes metal ions such as Cu
2+ that catalyses the destruction of hydrazine by reaction with monochloramine (NH
2Cl) to produce
ammonium chloride and nitrogen.
Hydrogen azide (HN
3) was first produced in 1890 by the oxidation of aqueous hydrazine by nitrous acid. It is very explosive and even dilute solutions can be dangerous. It has a disagreeable and irritating smell and is a potentially lethal (but not cumulative) poison. It may be considered the conjugate acid of the azide anion, and is similarly analogous to the hydrohalic acids.
Halides and oxohalides
![Nitrogen trichloride](https://upload.wikimedia.org/wikipedia/commons/1/16/Nitrogen_trichloride.JPG)
All four simple nitrogen trihalides are known. A few mixed halides and hydrohalides are known, but are mostly unstable; examples include NClF
2, NCl
2F, NBrF
2, NF
2H, fluoroamine, NFH
2, Dichloramine, NCl
2H, and Monochloramine, NClH
2.
[Greenwood and Earnshaw, pp. 438–42]
Five nitrogen fluorides are known. Nitrogen trifluoride (NF
3, first prepared in 1928) is a colourless and odourless gas that is thermodynamically stable, and most readily produced by the electrolysis of molten ammonium fluoride dissolved in anhydrous hydrogen fluoride. Like carbon tetrafluoride, it is not at all reactive and is stable in water or dilute aqueous acids or alkalis. Only when heated does it act as a fluorinating agent, and it reacts with copper, arsenic, antimony, and bismuth on contact at high temperatures to give tetrafluorohydrazine (N
2F
4). The cations and are also known (the latter from reacting tetrafluorohydrazine with strong fluoride-acceptors such as arsenic pentafluoride), as is ONF
3, which has aroused interest due to the short N–O distance implying partial double bonding and the highly polar and long N–F bond. Tetrafluorohydrazine, unlike hydrazine itself, can dissociate at room temperature and above to give the radical NF
2•. Fluorine azide (FN
3) is very explosive and thermally unstable. Dinitrogen difluoride (N
2F
2) exists as thermally interconvertible ''cis'' and ''trans'' isomers, and was first found as a product of the thermal decomposition of FN
3.
Nitrogen trichloride (NCl
3) is a dense, volatile, and explosive liquid whose physical properties are similar to those of carbon tetrachloride, although one difference is that NCl
3 is easily hydrolysed by water while CCl
4 is not. It was first synthesised in 1811 by Pierre Louis Dulong, who lost three fingers and an eye to its explosive tendencies. As a dilute gas it is less dangerous and is thus used industrially to bleach and sterilise flour. Nitrogen tribromide (NBr
3), first prepared in 1975, is a deep red, temperature-sensitive, volatile solid that is explosive even at −100 °C. Nitrogen triiodide (NI
3) is still more unstable and was only prepared in 1990. Its adduct with ammonia, which was known earlier, is very shock-sensitive: it can be set off by the touch of a feather, shifting air currents, or even
alpha particle
Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be pr ...
s.
For this reason, small amounts of nitrogen triiodide are sometimes synthesised as a demonstration to high school chemistry students or as an act of "chemical magic". Chlorine azide (ClN
3) and bromine azide (BrN
3) are extremely sensitive and explosive.
Two series of nitrogen oxohalides are known: the nitrosyl halides (XNO) and the nitryl halides (XNO
2). The first is very reactive gases that can be made by directly halogenating nitrous oxide. Nitrosyl fluoride (NOF) is colourless and a vigorous fluorinating agent. Nitrosyl chloride (NOCl) behaves in much the same way and has often been used as an ionising solvent. Nitrosyl bromide (NOBr) is red. The reactions of the nitryl halides are mostly similar: nitryl fluoride (FNO
2) and nitryl chloride (ClNO
2) are likewise reactive gases and vigorous halogenating agents.
Oxides
![Nitrogen dioxide at different temperatures](https://upload.wikimedia.org/wikipedia/commons/6/60/Nitrogen_dioxide_at_different_temperatures.jpg)
Nitrogen forms nine molecular oxides, some of which were the first gases to be identified: N
2O (nitrous oxide), NO (
nitric oxide), N
2O
3 (dinitrogen trioxide), NO
2 (nitrogen dioxide), N
2O
4 (dinitrogen tetroxide), N
2O
5 (dinitrogen pentoxide), N
4O (nitrosylazide),
[Greenwood and Earnshaw, pp. 443–58] and N(NO
2)
3 (trinitramide). All are thermally unstable towards decomposition to their elements. One other possible oxide that has not yet been synthesised is oxatetrazole (N
4O), an aromatic ring.
Nitrous oxide (N
2O), better known as laughing gas, is made by thermal decomposition of molten ammonium nitrate at 250 °C. This is a redox reaction and thus nitric oxide and nitrogen are also produced as byproducts. It is mostly used as a propellant and aerating agent for cream, sprayed canned whipped cream, and was formerly commonly used as an anaesthetic. Despite appearances, it cannot be considered to be the inorganic anhydride, anhydride of hyponitrous acid (H
2N
2O
2) because that acid is not produced by the dissolution of nitrous oxide in water. It is rather unreactive (not reacting with the halogens, the alkali metals, or ozone at room temperature, although reactivity increases upon heating) and has the unsymmetrical structure N–N–O (N≡N
+O
−↔
−N=N
+=O): above 600 °C it dissociates by breaking the weaker N–O bond.
Nitric oxide (NO) is the simplest stable molecule with an odd number of electrons. In mammals, including humans, it is an important cellular signaling molecule involved in many physiological and pathological processes. It is formed by catalytic oxidation of ammonia. It is a colourless paramagnetic gas that, being thermodynamically unstable, decomposes to nitrogen and oxygen gas at 1100–1200 °C. Its bonding is similar to that in nitrogen, but one extra electron is added to a ''π''* antibonding orbital and thus the bond order has been reduced to approximately 2.5; hence dimerisation to O=N–N=O is unfavourable except below the boiling point (where the ''cis'' isomer is more stable) because it does not actually increase the total bond order and because the unpaired electron is delocalised across the NO molecule, granting it stability. There is also evidence for the asymmetric red dimer O=N–O=N when nitric oxide is condensed with polar molecules. It reacts with oxygen to give brown nitrogen dioxide and with halogens to give nitrosyl halides. It also reacts with transition metal compounds to give nitrosyl complexes, most of which are deeply coloured.
Blue dinitrogen trioxide (N
2O
3) is only available as a solid because it rapidly dissociates above its melting point to give nitric oxide, nitrogen dioxide (NO
2), and dinitrogen tetroxide (N
2O
4). The latter two compounds are somewhat difficult to study individually because of the equilibrium between them, although sometimes dinitrogen tetroxide can react by heterolytic fission to nitrosonium and
nitrate in a medium with high dielectric constant. Nitrogen dioxide is an acrid, corrosive brown gas. Both compounds may be easily prepared by decomposing a dry metal nitrate. Both react with water to form
nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...
. Dinitrogen tetroxide is very useful for the preparation of anhydrous metal nitrates and nitrato complexes, and it became the storable oxidiser of choice for many rockets in both the United States and USSR by the late 1950s. This is because it is a hypergolic propellant in combination with a
hydrazine-based Rocket propellant, rocket fuel and can be easily stored since it is liquid at room temperature.
The thermally unstable and very reactive dinitrogen pentoxide (N
2O
5) is the anhydride of
nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...
, and can be made from it by dehydration with phosphorus pentoxide. It is of interest for the preparation of explosives. It is a deliquescent, colourless crystalline solid that is sensitive to light. In the solid state it is ionic with structure [NO
2]
+[NO
3]
−; as a gas and in solution it is molecular O
2N–O–NO
2. Hydration to nitric acid comes readily, as does analogous reaction with hydrogen peroxide giving peroxonitric acid (HOONO
2). It is a violent oxidising agent. Gaseous dinitrogen pentoxide decomposes as follows:
:N
2O
5 NO
2 + NO
3 → NO
2 + O
2 + NO
:N
2O
5 + NO 3 NO
2
Oxoacids, oxoanions, and oxoacid salts
Many nitrogen oxoacids are known, though most of them are unstable as pure compounds and are known only as aqueous solutions or as salts. Hyponitrous acid (H
2N
2O
2) is a weak diprotic acid with the structure HON=NOH (p''K''
a1 6.9, p''K''
a2 11.6). Acidic solutions are quite stable but above pH 4 base-catalysed decomposition occurs via [HONNO]
− to nitrous oxide and the hydroxide anion. Hyponitrites (involving the anion) are stable to reducing agents and more commonly act as reducing agents themselves. They are an intermediate step in the oxidation of ammonia to nitrite, which occurs in the
nitrogen cycle. Hyponitrite can act as a bridging or chelating bidentate ligand.
[Greenwood and Earnshaw, pp. 459–72]
Nitrous acid (HNO
2) is not known as a pure compound, but is a common component in gaseous equilibria and is an important aqueous reagent: its aqueous solutions may be made from acidifying cool aqueous
nitrite (, bent) solutions, although already at room temperature disproportionation to
nitrate and nitric oxide is significant. It is a weak acid with p''K''
''a'' 3.35 at 18 °C. They may be titration, titrimetrically analysed by their oxidation to nitrate by permanganate. They are readily reduced to nitrous oxide and nitric oxide by sulfur dioxide, to hyponitrous acid with tin(II), and to ammonia with hydrogen sulfide. Salts of hydrazinium react with nitrous acid to produce azides which further react to give nitrous oxide and nitrogen. Sodium nitrite is mildly toxic in concentrations above 100 mg/kg, but small amounts are often used to cure meat and as a preservative to avoid bacterial spoilage. It is also used to synthesise hydroxylamine and to diazotise primary aromatic amines as follows:
:ArNH
2 + HNO
2 → [ArNN]Cl + 2 H
2O
Nitrite is also a common ligand that can coordinate in five ways. The most common are nitro (bonded from the nitrogen) and nitrito (bonded from an oxygen). Nitro-nitrito isomerism is common, where the nitrito form is usually less stable.
![Fuming nitric acid 40ml](https://upload.wikimedia.org/wikipedia/commons/5/53/Fuming_nitric_acid_40ml.jpg)
Nitric acid (HNO
3) is by far the most important and the most stable of the nitrogen oxoacids. It is one of the three most used acids (the other two being sulfuric acid and
hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid
Acid strength is the tendency of an acid, symbol ...
) and was first discovered by alchemists in the 13th century. It is made by the catalytic oxidation of ammonia to nitric oxide, which is oxidised to nitrogen dioxide, and then dissolved in water to give concentrated nitric acid. In the United States, United States of America, over seven million tonnes of nitric acid are produced every year, most of which is used for nitrate production for fertilisers and explosives, among other uses. Anhydrous nitric acid may be made by distilling concentrated nitric acid with phosphorus pentoxide at low pressure in glass apparatus in the dark. It can only be made in the solid state, because upon melting it spontaneously decomposes to nitrogen dioxide, and liquid nitric acid undergoes Molecular autoionization, self-ionisation to a larger extent than any other covalent liquid as follows:
:2 HNO
3 + H
2O + [NO
2]
+ + [NO
3]
−
Two hydrates, HNO
3·H
2O and HNO
3·3H
2O, are known that can be crystallised. It is a strong acid and concentrated solutions are strong oxidising agents, though
gold
Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile me ...
, platinum, rhodium, and iridium are immune to attack. A 3:1 mixture of concentrated hydrochloric acid and nitric acid, called ''
aqua regia'', is still stronger and successfully dissolves gold and platinum, because free chlorine and nitrosyl chloride are formed and chloride anions can form strong complexes. In concentrated sulfuric acid, nitric acid is protonated to form nitronium, which can act as an electrophile for aromatic nitration:
:HNO
3 + 2 H
2SO
4 + H
3O
+ + 2
The thermal stabilities of
nitrates (involving the trigonal planar anion) depends on the basicity of the metal, and so do the products of decomposition (thermolysis), which can vary between the nitrite (for example, sodium), the oxide (potassium and lead), or even the metal itself (silver) depending on their relative stabilities. Nitrate is also a common ligand with many modes of coordination.
Finally, although orthonitric acid (H
3NO
4), which would be analogous to orthophosphoric acid, does not exist, the tetrahedral orthonitrate anion is known in its sodium and potassium salts:
:
NaNO3 + Na2O ->[\ce][\ce] Na3NO4
These white crystalline salts are very sensitive to water vapour and carbon dioxide in the air:
:Na
3NO
4 + H
2O + CO
2 → NaNO
3 + NaOH + NaHCO
3
Despite its limited chemistry, the orthonitrate anion is interesting from a structural point of view due to its regular tetrahedral shape and the short N–O bond lengths, implying significant polar character to the bonding.
Organic nitrogen compounds
Nitrogen is one of the most important elements in organic chemistry. Many organic functional groups involve a carbon–nitrogen bond, such as amides (RCONR
2), amines (R
3N), imines (RC(=NR)R), imides (RCO)
2NR,
azides (RN
3),
azo compound
Azo compounds are organic compounds bearing the functional group diazenyl (, in which R and R′ can be either aryl or alkyl groups).
IUPAC defines azo compounds as: "Derivatives of diazene (diimide), , wherein both hydrogens are substituted ...
s (RN
2R),
cyanate
Cyanate is an anion with the structural formula , usually written . It also refers to any salt containing it, such as ammonium cyanate.
It is an isomer of the much less stable fulminate anion .William R. Martin and David W. Ball (2019): "Sma ...
s and isocyanates (ROCN or RCNO),
nitrates (RONO
2), nitriles and isonitriles (RCN or RNC),
nitrites (RONO), nitro compounds (RNO
2), nitroso compounds (RNO), oximes (RCR=NOH), and pyridine derivatives. C–N bonds are strongly polarised towards nitrogen. In these compounds, nitrogen is usually trivalent (though it can be tetravalent in quaternary ammonium salts, R
4N
+), with a lone pair that can confer basicity on the compound by being coordinated to a proton. This may be offset by other factors: for example, amides are not basic because the lone pair is delocalised into a double bond (though they may act as acids at very low pH, being protonated at the oxygen), and pyrrole is not acidic because the lone pair is delocalised as part of an aromaticity, aromatic ring.
The amount of nitrogen in a chemical substance can be determined by the Kjeldahl method. In particular, nitrogen is an essential component of nucleic acids,
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
s and thus
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s, and the energy-carrying molecule
adenosine triphosphate
Adenosine triphosphate (ATP) is an organic compound that provides energy to drive many processes in living cells, such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis. Found in all known forms o ...
and is thus vital to all life on Earth.
Occurrence
![Nitrogen Cycle](https://upload.wikimedia.org/wikipedia/commons/f/fe/Nitrogen_Cycle.svg)
Nitrogen is the most common pure element in the earth, making up 78.1% of the volume of the Atmosphere of Earth, atmosphere
(75.5% by mass), around 3.89 million gigatonnes. Despite this, it is Abundance of elements in Earth's crust, not very abundant in Earth's crust, making up somewhere around 19 parts per million of this, on par with niobium, gallium, and
lithium
Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid ...
. (This represents 300,000 to a million gigatonnes of nitrogen, depending on the mass of the crust.) The only important nitrogen minerals are
nitre
Niter or nitre is the mineral form of potassium nitrate, KNO3. It is a soft, white, highly soluble mineral found primarily in arid climates or cave deposits.
Historically, the term ''niter'' was not well differentiated from natron, both of w ...
(
potassium nitrate
Potassium nitrate is a chemical compound with the chemical formula . This alkali metal nitrate salt is also known as Indian saltpetre (large deposits of which were historically mined in India). It is an ionic salt of potassium ions K+ and nitr ...
, saltpetre) and sodanitre, soda nitre (
sodium nitrate, Chilean saltpetre). However, these have not been an important source of nitrates since the 1920s, when the industrial synthesis of ammonia and nitric acid became common.
[Greenwood and Earnshaw, pp. 407–09]
Nitrogen compounds constantly interchange between the atmosphere and living organisms. Nitrogen must first be processed, or "nitrogen fixation, fixed", into a plant-usable form, usually ammonia. Some nitrogen fixation is done by lightning strikes producing the nitrogen oxides, but most is done by diazotrophic bacteria through enzymes known as
nitrogenase
Nitrogenases are enzymes () that are produced by certain bacteria, such as cyanobacteria (blue-green bacteria) and rhizobacteria. These enzymes are responsible for the reduction of nitrogen (N2) to ammonia (NH3). Nitrogenases are the only fa ...
s (although today industrial nitrogen fixation to ammonia is also significant). When the ammonia is taken up by plants, it is used to synthesise proteins. These plants are then digested by animals who use the nitrogen compounds to synthesise their proteins and excrete nitrogen-bearing waste. Finally, these organisms die and decompose, undergoing bacterial and environmental oxidation and
denitrification
Denitrification is a microbially facilitated process where nitrate (NO3−) is reduced and ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products. Facultative anaerobic bacteria perform denitr ...
, returning free dinitrogen to the atmosphere. Industrial nitrogen fixation by the
Haber process
The Haber process, also called the Haber–Bosch process, is an artificial nitrogen fixation process and is the main industrial procedure for the production of ammonia today. It is named after its inventors, the German chemists Fritz Haber and ...
is mostly used as fertiliser, although excess nitrogen–bearing waste, when leached, leads to
eutrophication
Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...
of freshwater and the creation of marine Dead zone (ecology), dead zones, as nitrogen-driven bacterial growth depletes water oxygen to the point that all higher organisms die. Furthermore, nitrous oxide, which is produced during denitrification, attacks the atmospheric ozone layer.
Many saltwater fish manufacture large amounts of trimethylamine oxide to protect them from the high osmosis, osmotic effects of their environment; conversion of this compound to dimethylamine is responsible for the early odour in unfresh saltwater fish. In animals, free radical
nitric oxide (derived from an
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
), serves as an important regulatory molecule for circulation.
Nitric oxide's rapid reaction with water in animals results in the production of its metabolite
nitrite. Animal metabolism of nitrogen in proteins, in general, results in the excretion of urea, while animal metabolism of nucleic acids results in the excretion of urea and uric acid. The characteristic odour 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.
Production
Nitrogen gas is an industrial gas produced by the fractional distillation of liquid air, or by mechanical means using gaseous air (pressurised reverse Osmotic pressure, osmosis membrane or pressure swing adsorption). Nitrogen gas generators using membranes or pressure swing adsorption (PSA) are typically more cost and energy efficient than bulk-delivered nitrogen. Commercial nitrogen is often a byproduct of air-processing for industrial concentration of
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
for steelmaking and other purposes. When supplied compressed in cylinders it is often called OFN (oxygen-free nitrogen). Commercial-grade nitrogen already contains at most 20 ppm oxygen, and specially purified grades containing at most 2 ppm oxygen and 10 ppm
argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as ...
are also available.
[Greenwood and Earnshaw, pp. 409–11]
In a chemical laboratory, it is prepared by treating an aqueous solution of
ammonium chloride with sodium nitrite.
:NH
4Cl + NaNO
2 → N
2 + NaCl + 2 H
2O
Small amounts of the impurities NO and HNO
3 are also formed in this reaction. The impurities can be removed by passing the gas through aqueous sulfuric acid containing potassium dichromate.
Very pure nitrogen can be prepared by the thermal decomposition of barium azide or sodium azide.
:2 NaN
3 → 2 Na + 3 N
2
Applications
Gas
The applications of nitrogen compounds are naturally extremely widely varied due to the huge size of this class: hence, only applications of pure nitrogen itself will be considered here. Two-thirds (2/3) of nitrogen produced by industry is sold as gas and the remaining one-third (1/3) as a liquid.
The gas is mostly used as a low reactivity safe atmosphere wherever the oxygen in the air would pose a fire, explosion, or oxidising hazard. Some examples include:
* As a modified atmosphere, pure or mixed with
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
, to nitrogenate and preserve the freshness of packaged or bulk foods (by delaying Rancidification, rancidity and other forms of Redox, oxidative damage). Pure nitrogen as food additive is labeled in the European Union with the E number E941.
* In incandescent light bulbs as an inexpensive alternative to
argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as ...
.
* In Gaseous fire suppression, fire suppression systems for Information technology (IT) equipment.
* In the manufacture of stainless steel.
* In the case-hardening of steel by nitriding.
* In some aircraft fuel systems to reduce fire hazard (see inerting system).
* To inflate race car and aircraft tires, reducing the problems of inconsistent expansion and contraction caused by moisture and Redox, oxygen in natural air.
Nitrogen is commonly used during sample preparation in chemical analysis. It is used to concentrate and reduce the volume of liquid samples. Directing a pressurised stream of nitrogen gas perpendicular to the surface of the liquid causes the solvent to evaporate while leaving the solute(s) and un-evaporated solvent behind.
Nitrogen can be used as a replacement, or in combination with,
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
to pressurise kegs of some beers, particularly stouts and British ales, due to the smaller liquid bubble, bubbles it produces, which makes the dispensed beer smoother and beer head, headier. A pressure-sensitive nitrogen capsule known commonly as a "widget (beer), widget" allows nitrogen-charged beers to be packaged in Beverage can, cans and bottles. Nitrogen tanks are also replacing carbon dioxide as the main power source for paintball guns. Nitrogen must be kept at a higher pressure than CO
2, making N
2 tanks heavier and more expensive.
Equipment
Some construction equipment uses pressurized nitrogen gas to help Hydraulics, hydraulic system to provide extra power to devices such as Breaker (hydraulic), hydraulic hammer. Nitrogen gas, formed from the decomposition of sodium azide, is used for the inflation of airbags.
Execution
As nitrogen is an asphyxiant gas, some jurisdictions have considered asphyxiation by inhalation of pure nitrogen as a means of capital punishment (as a substitute for lethal injection).
However, , no executions using nitrogen gas have yet been carried out by any jurisdiction, and at least one jurisdiction (Capital punishment in Oklahoma, Oklahoma) which had considered nitrogen asphyxiation as an execution protocol had abandoned the effort.
Liquid
Liquid nitrogen is a cryogen, cryogenic liquid which looks like
water
Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
. When insulated in proper containers such as dewar flasks, it can be transported and stored with a low rate of evaporation, evaporative loss.
![A cylinder container, containing liquid nitrogen](https://upload.wikimedia.org/wikipedia/commons/4/48/A_cylinder_container%2C_containing_liquid_nitrogen.jpg)
Like dry ice, the main use of liquid nitrogen is for cooling to low temperatures. It is used in the cryopreservation of biological materials such as blood and reproductive cells (sperm and ovum, eggs). It is used in cryotherapy to remove cysts and warts on the skin by freezing them. It is used in laboratory cold traps, and in cryopumps to obtain lower pressures in vacuum pumped systems. It is used to cool heat-sensitive electronics such as infrared detectors and X-ray detectors. Other uses include freeze-grinding and machining materials that are soft or rubbery at room temperature, shrink-fitting and assembling engineering components, and more generally to attain very low temperatures where necessary. Because of its low cost, liquid nitrogen is often used for cooling even when such low temperatures are not strictly necessary, such as refrigeration of food, freeze-branding livestock, freezing pipes to halt flow when valves are not present, and consolidating unstable soil by freezing whenever excavation is going on underneath.
Safety
Gas
Although nitrogen is non-toxic, when released into an enclosed space it can displace oxygen, and therefore presents an Nitrogen asphyxiation, asphyxiation hazard. This may happen with few warning symptoms, since the human carotid body is a relatively poor and slow low-oxygen (hypoxia) sensing system. An example occurred shortly before the launch of the STS-1, first Space Shuttle mission on March 19, 1981, when two technicians died from asphyxiation after they walked into a space located in the Mobile launcher platform#Saturn V and Space Shuttle, Space Shuttle's mobile launcher platform that was pressurised with pure nitrogen as a precaution against fire.
When inhaled at high partial pressures (more than about 4 bar, encountered at depths below about 30 m in scuba diving), nitrogen is an anesthetic agent, causing nitrogen narcosis, a temporary state of mental impairment similar to nitrous oxide intoxication.
Nitrogen dissolves in the blood and body fats. Rapid decompression (as when divers ascend too quickly or astronauts decompress 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''), when nitrogen bubbles form in the bloodstream, nerves, joints, and other sensitive or vital areas.
Bubbles from other "inert" gases (gases other than carbon dioxide and oxygen) cause the same effects, so replacement of nitrogen in breathing gases may prevent nitrogen narcosis, but does not prevent decompression sickness.
Liquid
As a cryogenic liquid, liquid nitrogen can be dangerous by causing cold burns on contact, although the Leidenfrost effect provides protection for very short exposure (about one second). Ingestion of liquid nitrogen can cause severe internal damage. For example, in 2012, a young woman in England had to have her stomach removed after ingesting a cocktail made with liquid nitrogen.
Because the liquid-to-gas expansion ratio of nitrogen is 1:694 at 20 °C, a tremendous amount of force can be generated if liquid nitrogen is rapidly vaporised in an enclosed space. In an incident on January 12, 2006, at Texas A&M University, the pressure-relief devices of a tank of liquid nitrogen were malfunctioning and later sealed. As a result of the subsequent pressure buildup, the tank failed catastrophically. The force of the explosion was sufficient to propel the tank through the ceiling immediately above it, shatter a reinforced concrete beam immediately below it, and blow the walls of the laboratory 0.1–0.2 m off their foundations.
Liquid nitrogen readily evaporates to form gaseous nitrogen, and hence the precautions associated with gaseous nitrogen also apply to liquid nitrogen.
[British Compressed Gases Association (2000) BCGA Code of Practice CP30]
The Safe Use of Liquid nitrogen Dewars up to 50 litres.
. For example, oxygen sensors are sometimes used as a safety precaution when working with liquid nitrogen to alert workers of gas spills into a confined space.
Vessels containing liquid nitrogen can liquid oxygen, condense oxygen from air. The liquid in such a vessel becomes increasingly enriched in oxygen (boiling point −183 °C, higher than that of nitrogen) as the nitrogen evaporates, and can cause violent oxidation of organic material.
Oxygen deficiency monitors
Oxygen deficiency monitors are used to measure levels of oxygen in confined spaces and any place where nitrogen gas or liquid are stored or used. In the event of a nitrogen leak, and a decrease in oxygen to a pre-set alarm level, an oxygen deficiency monitor can be programmed to set off audible and visual alarms, thereby providing notification of the possible impending danger. Most commonly the oxygen range to alert personnel is when oxygen levels get below 19.5%. OSHA specifies that a hazardous atmosphere may include one where the oxygen concentration is below 19.5% or above 23.5%.
[National Institutes of Health. Protocol for Use and Maintenance of Oxygen Monitoring Devices. February 2014, at 1:35 UTC. Available at: https://www.ors.od.nih.gov/sr/dohs/documents/protocoloxygenmonitoring.pdf . Accessed June 23, 2020]
Oxygen deficiency monitors can either be fixed, mounted to the wall and hard-wired into the building's power supply or simply plugged into a power outlet, or a portable hand-held or wearable monitor.
See also
* Reactive nitrogen species
* Soil gas
References
Bibliography
*
External links
Etymology of Nitrogenat ''The Periodic Table of Videos'' (University of Nottingham)
Nitrogen podcastfrom the Royal Society of Chemistry's ''Chemistry World''
{{good article
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Chemical elements
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Reactive nonmetals
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