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Nitrogen

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Nitrogen is a chemical element in the periodic table that has the symbol N and atomic number 7. A common normally colorless, odorless, tasteless and mostly inert diatomic non-metal gas, nitrogen constitutes 78 percent of Earth's atmosphere and is a constituent of all living tissues. Nitrogen forms many important compounds such as ammonia, nitric acid, and cyanides.


CarbonNitrogenOxygen
 
N
P  
 
 
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General
Name, Symbol, NumberNitrogen, N, 7
Chemical series nonmetals
Group, Period, Block15 (VA), 2 , p
Density, Hardness 1.2506 kg/m3(273K), NA
Appearance colorless
125px
Atomic properties
Atomic weight 14.0067 amu
Atomic radius (calc.) 65 (56) pm
Covalent radius 75 pm
van der Waals radius 155 pm
Electron configuration [He]2s2s22p3
e- 's per energy level2, 5
Oxidation states (Oxide) ±3,5,4,2 (strong acid)
Crystal structure hexagonal
Physical properties
State of matter gas (__)
Melting point 63.14 K (-345.75 ðF)
Boiling point 77.35 K (-320.17 ðF)
Molar volume 13.54 ×1010-6 m3/mol
Heat of vaporization 2.7928 kJ/mol
Heat of fusion 0.3604 kJ/mol
Vapor pressure ND Pa at __ K
Speed of sound 334 m/s at 298.15 K
Miscellaneous
Electronegativity 3.04 (Pauling scale)
Specific heat capacity 1040 J/(kg*K)
Electrical conductivity ND 106/m ohm
Thermal conductivity 0.02598 W/(m*K)
1st ionization potential 1402.3 kJ/mol
2nd ionization potential 2856 kJ/mol
3rd ionization potential 4578.1 kJ/mol
4th ionization potential 7475.0 kJ/mol
5th ionization potential 9444.9 kJ/mol
6th ionization potential 53266.6 kJ/mol
7th ionization potential 64360 kJ/mol
Most stable isotopes
isoNAhalf-life DMDE MeVDP
13N{syn.}9.965 me capture2.22013C
14N99.634%N is stable with 7 neutrons
15N0.366%N is stable with 8 neutrons
SI units & STP are used except where noted.

Table of contents
1 Notable characteristics
2 Applications
3 History
4 Occurrence
5 Compounds
6 Biological role
7 Isotopes
8 Precautions
9 See also
10 Reference
11 External links

Notable characteristics

Nitrogen is a non-metal, with an electronegativity of 3.0. It has five electrons in its outer shell, so is trivalent in most compounds. Pure nitrogen is an unreactive colorless diatomic gas at room temperature, and comprises about 78% of the Earth's atmosphere. It condenses at 77 K and freezes at 63 K. Liquid nitrogen is a common cryogen.

Applications

The greatest single commercial use of nitrogen is as a component in the manufacture of ammonia via the Haber process. Ammonia is subsequently used for fertilizer production and to produce nitric acid. Nitrogen is used as an inert atmosphere in tanks of explosive liquids, during production of electronic parts such as transistors, diodes, and integrated circuits, and is used in the manufacture of stainless steel. Nitrogen is used as a coolant both for the immersion freezing of food products and for transportation of foods, for the preservation of bodies and reproductive cells (sperm and egg), and for the stable storage of biological samples in biology.

The salts of nitric acid include some important compounds, for example potassium nitrate, or saltpeter, and ammonium nitrate. The former compound is a component of gunpowder, the latter important in fertilizer. Nitrated organic compounds, such as nitroglycerin and trinitrotoluene, are often explosives.

Nitric acid is used as an oxidizer in liquid fueled rockets. Hydrazine and hydrazine derivatives find use as rocket fuels.

Nitrogen in its liquid state (often referred to as LN2) is often used in cryogenics. Liquid nitrogen is produced by distillation from liquid air. At atmospheric pressure, nitrogen condenses at -195.8 degrees Celsius. (-320.4 degrees Fahrenheit). It is the liquid coolant frequently used for demonstrations in science education.

History

Nitrogen (Latin nitrum, Greek Nitron meaning "native soda", "genes", "forming") is formally considered to have been discovered by Daniel Rutherford in 1772, who called it noxious air or phlogisticated 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 dephlogisticated air. Nitrogen gas was inert enough that Antoine Lavoisier referred to it as azote, which stands for without life.

Compounds of nitrogen were known in the Middle Ages. The alchemists knew nitric acid as aqua fortis. The mixture of nitric and hydrochloric acids was known as aqua regia, celebrated for its ability to dissolve gold.

Occurrence

Nitrogen is the largest single component of the Earth's atmosphere (78.1% by volume, 75.5% by weight) and is acquired for industrial purposes by the fractional distillation of liquid air. Compounds that contain this element have been observed in outer space. Nitrogen-14 is created as part of the fusion processes in stars. Nitrogen is a large component of animal waste (for example, guano), usually in the form of urea, uric acid, and compounds of these nitrogenous products.

Molecular nitrogen has been known to occur in Titan's atmosphere for some time, and has now been detected in interstellar space by David Knauth and coworkers using the Far Ultraviolet Spectroscopic Explorer.

Compounds

The main hydride of nitrogen is ammonia (NH3) although hydrazine (N2H4) is also well known. Ammonia is somewhat more basic than water, and in solution forms ammonium ions (NH4+). Liquid ammonia in fact slightly amphiprotic and forms ammonium and amide ions (NH2-); both amides and nitride (N3-) salts are known, but decompose in water. Singly and doubly substituted compounds of ammonia are called amines. Larger chains, rings and structures of nitogen hydrides are also known but virtually unstable.

Other classes of nitrogen anions are azides (N3-), which are linear and isoelectronic to carbon dioxide. Another molecule of the same structure is dinitrogen monoxide (N2O), or laughing gas. This is one of a variety of oxides, the most prominent of which are nitrogen monoxide (NO) and nitrogen dioxide (NO2), which both contain an unpaired electron. The latter shows some tendency to dimerize and is an important component of smog.

The more standard oxides, dinitrogen trioxide (N2O3) and dinitrogen pentoxide (N2O5), are actually fairly unstable and explosive. The corresponding acids are nitrous (HNO2) and nitric acid (HNO3), with the corresponding salts called nitrites and nitrates. Nitric acid is one of the few acids stronger than hydronium.

Biological role

Nitrogen is an essential part of amino and nucleic acids which makes nitrogen vital to all life. Legumes like the soybean plant, can recover nitrogen directly from the atmosphere because their roots have nodules harboring microbes that do the actual conversion to ammonia in a process known as nitrogen fixation. The legume subsequently converts ammonia to nitrogen oxides and amino acids to form proteins.

Isotopes

There are two stable isotopes: N-14 and N-15. By far the most common is N-14 (99.634%), which is produced in the CNO cycle in stars. The rest is N-15. Of the ten isotopes produced synthetically, one has a half life of nine minutes and the remaining isotopes have half lives on the order of seconds or less. Biologically-mediated reactions (e.g., assimilation, nitrification, and denitrification) strongly control nitrogen dynamics in the soil. These reactions almost always result in N-15 enrichment of the substrate and depletion of the product. Although precipitation often contains subequal quantities of ammonium and nitrate, because ammonium is preferentially retained by the canopy relative to atmospheric nitrate, most of the atmospheric nitrogen that reaches the soil surface is in the form of nitrate. Soil nitrate is preferentially assimilated by tree roots relative to soil ammonium.

Precautions

Nitrate fertilizer washoff is a major source of ground water and river pollution. Cyano (-CNN) containing compounds form extremely poisonous salts and are deadly to many animals and all mammals.

See also

Reference

External links