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Nitrogen

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7 carbonnitrogenoxygen
-

N

P
General
Name, symbol, number nitrogen, N, 7
Chemical series nonmetals
Group, period, block 152, p
Appearance colorless gas
Standard atomic weight 14.007(2)g·mol−1
Electron configuration 1s2 2s2 2p3
Electrons per shell 2, 5
Physical properties
Phase gas
Density (0 °C, 101.325 kPa)
1.251 g/L
Melting point 63.15 K
(-210.00 °C, -346.00 °F)
Boiling point 77.36 K
(-195.79 °C, -320.42 °F)
Critical point 126.21 K, 3.39 MPa
Heat of fusion (N2) 0.360 kJ·mol−1
Heat of vaporization (N2) 5.56 kJ·mol−1
Heat capacity (25 °C) (N2)
29.124 J·mol−1·K−1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 37 41 46 53 62 77
Atomic properties
Crystal structure hexagonal
Oxidation states 5, 4, 3, 2, 1,[1], -1, -3
(strongly acidic oxide)
Electronegativity 3.04 (Pauling scale)
Ionization energies
(more)
1st: 1402.3 kJ·mol−1
2nd: 2856 kJ·mol−1
3rd: 4578.1 kJ·mol−1
Atomic radius 65 pm
Atomic radius (calc.) 56 pm
Covalent radius 75 pm
Van der Waals radius 155 pm
Miscellaneous
Magnetic ordering diamagnetic
Thermal conductivity (300 K) 25.83 × 10−3 W·m−1·K−1
Speed of sound (gas, 27 °C) 353 m/s
CAS registry number 7727-37-9
Selected isotopes
Main article: Isotopes of nitrogen
iso NA half-life DM DE (MeV) DP
13N syn 9.965 min ε 2.220 13C
14N 99.634% 14N is stable with 7 neutrons
15N 0.366% 15N is stable with 8 neutrons
References
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Nitrogen (pronounced /nī'trə-jən/) is a chemical element that has the symbol N and atomic number 7 and atomic weight 14.007. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78.1% by volume of Earth's atmosphere.

Many industrially important compounds, such as ammonia, nitric acid, organic nitrates (propellants and explosives), and cyanides, contain nitrogen. The very 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.

Nitrogen occurs in all living organisms — it is a constituent element of amino acids and thus of proteins, and of nucleic acids (DNA and RNA); resides in the chemical structure of almost all neurotransmitters; and is a defining component of alkaloids, biological molecules produced by many organisms.

Contents

Properties

Nitrogen is a nonmetal, with an electronegativity of 3.0. It has five electrons in its outer shell and is therefore trivalent in most compounds. The triple bond in molecular nitrogen (N2) is one of 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, 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 under diamond anvil conditions, nitrogen polymerizes into the single bonded diamond crystal structure, an allotrope nicknamed "nitrogen diamond."[2]

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.[citation needed]

Molecular nitrogen and nitrogen compounds have been detected in interstellar space by astronomers using the Far Ultraviolet Spectroscopic Explorer.[3] Molecular nitrogen is a major constituent of the Saturnian moon Titan's thick atmosphere, and occurs in trace amounts in other planetary atmospheres.[4]

Nitrogen is present in all living organisms in proteins, nucleic acids and other molecules. It is a large component of animal waste (for example, guano), usually in the form of urea, uric acid, ammonium compounds and derivatives of these nitrogenous products, which are essential nutrients for all plants that are unable to fix atmospheric nitrogen.

See also: Nitrate minerals and Ammonium minerals

Isotopes

See also: Isotopes of nitrogen

There are two stable isotopes of nitrogen: 14N and 15N. By far the most common is 14N (99.634%), which is produced in the CNO cycle in stars and the remaining is 15N. Of the ten isotopes produced synthetically, 13N has a half life of 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.

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).

History

Nitrogen (Latin nitrogenium, where nitrum (from Greek nitron) means "saltpetre" (see niter), and genes means "forming") is formally considered to have been discovered by Daniel Rutherford in 1772, who called it noxious air or fixed air. That there was a fraction of air that did not support combustion was well known to the late 18th century chemist. Nitrogen was also studied at about the same time by Carl Wilhelm Scheele, Henry Cavendish, and Joseph Priestley, who referred to it as burnt air or phlogisticated air. Nitrogen gas was inert enough that Antoine Lavoisier referred to it as azote, from the Greek word αζωτος meaning "lifeless". Animals died in it, and it was the principal component of air in which animals had suffocated and flames had burned to extinction. This term has become the French word for "nitrogen" and later spread out to many other languages.

Argon was discovered when it was noticed that nitrogen from air is not identical to nitrogen from chemical reactions.

Compounds of nitrogen were known in the Middle Ages. The alchemists knew nitric acid as aqua fortis (strong water). The mixture of nitric and hydrochloric acids was known as aqua regia (royal water), celebrated for its ability to dissolve gold (the king of metals). The earliest industrial and agricultural applications of nitrogen compounds involved uses in the form of saltpeter (sodium- or potassium nitrate), notably in gunpowder, and much later, as fertilizer,

Applications

Image:NitrogenRencer.png
A computer rendering of the nitrogen molecule, N2.

Nitrogen gas is acquired for industrial purposes by the fractional distillation of liquid air, or by mechanical means using gaseous air (i.e. pressurised reverse osmosis membrane or pressure swing adsorption). Commercial nitrogen is often a byproduct of air-processing for industrial concentration of oxygen for steelmaking and other purposes.

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

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