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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 |
| Most
stable isotopes |
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| 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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