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The Element
Nitrogen
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.
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| General |
| Name, Symbol, Number |
Nitrogen, N, 7 |
| Chemical series |
nonmetals |
| Group, Period, Block |
15 (VA), 2 , p |
| Density, Hardness |
1.2506 kg/m3(273K), NA |
| Appearance |
colorless
|
| 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]2s22p3 |
| e- 's per energy level |
2, 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 °F) |
| Boiling point |
77.35 K (-320.17 °F) |
| Molar volume |
13.54 ×10-6 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 |
| SI units & STP
are used except where noted. |
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 (-CN) containing compounds form extremely
poisonous salts and are deadly
to many animals and all mammals.
Reference
External links
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