Nitrogen

March 1, 2011, 5:06 pm
Content Cover Image

Vial of glowing ultrapure nitrogen, N2. Original size in cm: 1 x 5. Source: images-of-elements.com

Nitrogen is most commonly experienced in the form of molecular nitrogen (N2) as a colorless, odorless and inert gas that constitutes about nearly four fifths (78%) of air by volume.

Previous Element: Carbon

Next Element: Oxygen
14

N

14.0067
Physical Properties
Color colorless
Phase at Room Temp. gas
Density (g/cm3) 0.0012
Hardness (Mohs) ---
Melting Point (K) 63.34
Boiling Point (K) 77.4
Heat of Fusion (kJ/mol) 0.7
Heat of Vaporization (kJ/mol) 6
Heat of Atomization (kJ/mol) 473
Thermal Conductivity (J/m sec K) 0.03
Electrical Conductivity (1/mohm cm) 0
Source air
Atomic Properties
Electron Configuration  
Number of Isotopes 2
Electron Affinity (kJ/mol) -6.75
First Ionization Energy (kJ/mol) 1402.3
Second Ionization Energy (kJ/mol) 2856
Third Ionization Energy (kJ/mol) 4578
Electronegativity 3.04
Polarizability (Å3) 1.1
Atomic Weight 14.0067
Atomic Volume (cm3/mol) 17.3
Ionic Radius2- (pm) ---
Ionic Radius1- (pm) ---
Atomic Radius (pm) 70
Ionic Radius1+ (pm) ---
Ionic Radius2+ (pm) ---
Ionic Radius3+ (pm) 30
Common Oxidation Numbers -3, +3, +5
Other Oxid. Numbers -2, -1, +1, +2, +4
Abundance
In Earth's Crust (mg/kg) 1.9×101
In Earth's Ocean (mg/L) 5×10-1
In Human Body (%) 2.57%
Regulatory / Health
CAS Number 7727-37-9
OSHA Permissible Exposure Limit (PEL) No limits
OSHA PEL Vacated 1989 No limits
NIOSH Recommended Exposure Limit (REL) No limits
Sources:
Mineral Information Institute
Jefferson Accelerator Laboratory
EnvironmentalChemistry.com
 

The French chemist Antoine Laurent Lavoisier named nitrogen azote, meaning "without life." However, nitrogen compounds are found in foods, fertilizers, poisons, and explosives. As a liquid (boiling point = minus 195.8°C), molecular nitrogen is also colorless and odorless, and is similar in appearance to water. Nitrogen gas (N2) can be prepared by heating a water solution of ammonium nitrite (NH4NO3).

When nitrogen is heated it combines directly with magnesium, lithium and calcium. When mixed with oxygen and subjected to electric sparks, it forms first nitrogen monoxide (NO) and then nitrogen dioxide (NO2). When mixed with hydrogen and heated under pressure, ammonia is formed (the Haber Process).

History

The name derives from the Latin nitrum and Greek nitron for "native soda" and genes for "forming" because of nitrogen's presence in potassium nitrate (KNO), so called salpeter or nitre or native soda. It was discovered by the Scottish physician and chemist Daniel Rutherford in 1772. He removed oxygen and carbon dioxide from air and showed that the residual gas would not support combustion or living organisms. At the same time there were other noted scientists working on the problem of nitrogen. These included Scheele, Henry Cavendish, Joseph Priestley, and others. They called it “burnt" or "dephlogisticated air,” which meant air without oxygen.

Forms

Sodium nitrate (NaNO3) and potassium nitrate (KNO3) are formed by the decomposition of organic matter with compounds of these metals present. In certain dry areas of the world these saltpeters are found in quantity and are used as fertilizers. Other inorganic nitrogen compounds are nitric acid (HNO3), ammonia (NH3), the oxides (NO, NO2, N2O4, N2O), cyanides (CN-), etc.

Ammonia

caption Fertilizer factory in Myanmar.

Ammonia (NH3) is the most important commercial compound of nitrogen. It is typically produced by the Haber Process. Natural gas (methane, CH4) is reacted with steam to produce carbon dioxide (CO2) and hydrogen gas (H2) in a two step process. Hydrogen gas and nitrogen gas are then reacted in the Haber Process to produce ammonia.

CH4 + H2O → CO + 3H2

CO + H2O → CO2 + H2 + other reactions to ensure proper N2/H2 ratio

N2 + 3H2 → 2NH3

This colorless gas with a pungent odor is easily liquefied. In fact, the liquid is used as a nitrogen fertilizer. Ammonia is also used in the production of urea, NH2CONH2, which is used as a fertilizer, in the plastic industry, and in the livestock industry as a feed supplement. Ammonia is often the starting compound for many other nitrogen compounds.

Isotopes

Nitrogen exists as two stable isotopes, nitrogen-14 (14N) and nitrogen-15 (15N) that can be separated by chemical exchange or by thermal diffusion. Artificial radioactive isotopes have masses of 12, 13, 16, and 17. The most stable has a half-life of only about 10 minutes.

Sources

Nitrogen gas (N2) makes up 78.1% of the Earth’s air, by volume. The atmosphere of Mars, by comparison, is only 2.6% nitrogen. Nitrogen-14 (14N) is created as part of the fusion processes in stars.

Uses

Nitrogen has a wide range of uses. In addition to the manufacture of ammonia, its largest use, nitrogen is used in the electronics industry to flush air from vacuum tubes before the tubes are sealed. Incandescent lamp bulbs are flushed with nitrogen gas before being filled with a nitrogen-argon gas mixture. In metalworking operations, nitrogen is used to control furnace atmospheres during annealing (heating and slowly cooling metal for strengthening). Metalworkers also use nitrogen to remove dissolved hydrogen from molten aluminum and to refine scrap aluminum. Nitrogen is used to make a variety of explosives including ammonium nitrate, nitroglycerin, nitrocellulose, and trinitrotoluene (TNT). It is used as a refrigerant both for the immersion freezing of food products and for transportation of foods, and in liquid form it is used by the oil industry to build up pressure in wells to force crude oil to the surface.

Biological role

caption The soybean plant. (Source: U.S. Department of Agriculture)

The growth of all organisms depends on the availability of mineral nutrients, and none is more important than nitrogen, which is required in large amounts as an essential component of proteins, nucleic acids and other cellular constituents. The nitrogen cycle, whereby chemical processes make atmospheric nitrogen available for use in plants and animals and then is subsequently returned to the atmosphere, is a critical process for life. There is an abundant supply of nitrogen in the Earth's atmosphere—nearly 79% in the form of N2 gas. However, N2 is unavailable for use by most organisms because there is a triple bond between the two nitrogen atoms, making the molecule almost inert. In order for nitrogen to be used for growth it must be "fixed" (combined) in the form of ammonium (NH4) or nitrate (NO3) ions. The weathering of rocks releases these ions so slowly that it has a negligible effect on the availability of fixed nitrogen. So, nitrogen is often the limiting factor for growth and biomass production in all environments where there is suitable climate and availability of water to support life.

Microorganisms have a central role in almost all aspects of nitrogen availability and thus for life support on Earth. Some bacteria can convert N2 into ammonia (NH3) by the process termed nitrogen fixation; these bacteria are either free-living or form symbiotic associations with plants or other organisms (e.g., termites, protozoa). Legumes like the soybean plant, can recover nitrogen directly from the atmosphere because their roots have nodules that support microbes that do the actual conversion to ammonia. The legume subsequently converts ammonia to nitrogen oxides and amino acids to form proteins. Other bacteria bring about transformations of ammonia to nitrate, and of nitrate to N2 or other nitrogen gases. Many bacteria and fungi degrade organic matter, releasing fixed nitrogen for reuse by other organisms.

Environmental Effects

Nitrogen is the essential multi-media stressor. Its ubiquity in the environment and necessity to life assures its ease of transport through biotic and abiotic cycles and interaction with aquatic, atmospheric, and terrestrial systems. Excess nitrogen in the environment is associated with many large-scale environmental concerns, including, eutrophication of surface waters, toxic algae blooms, hypoxia, acid rain, nitrogen saturation in forests, and global warming.

Impact on water quality

caption Euthrophication in the Sea of Azov. (Source: NASA)

Nitrogen becomes a concern to water quality when nitrogen in the soil is converted to the nitrate (NO3-) form. It is a concern because nitrate is very mobile and easily moves with water in the soil. The concern of nitrates and water quality is generally directed at groundwater. However, nitrates can also enter surface waters such as ponds, streams and rivers. The presence of nitrates in the soil are largely the result of natural biological processes associated with the decomposition of plant residues and organic matter. Nitrates can also come from rainfall, animal manure and nitrogen fertilizers.

Whether or not nitrates actually enter groundwater depends on underlying soil and/or bedrock conditions, as well as the depth to groundwater. If depth to groundwater is shallow and the underlying soil is sandy, the potential for nitrates to enter groundwater is relatively high. However, if depth to groundwater is deep and the underlying soil is heavy clay, groundwater contamination from nitrates is not likely.

Once nitrates get into the groundwater, the greatest concerns are for infants less than one year old and for young or pregnant animals. High levels of nitrates can be toxic to newborns, causing anoxia, or internal suffocation. Seek alternative water sources if nitrate levels exceed the health standard of 10 ppm nitrate-N. Do not boil water to eliminate nitrates. It increases nitrate levels rather than decreasing them. The most common symptom of nitrate poisoning in babies is a bluish color to the skin, particularly around the baby's eyes and mouth. These symptoms of nitrate toxicity are commonly referred to as the Blue Baby Syndrome.

Impact on air quality

Nitrogen oxides, is the generic term for a group of reactive gases, all of which contain nitrogen and oxygen in varying amounts. Many of the nitrogen oxides are colorless and odorless. However, one common pollutant, nitrogen dioxide (NO2) along with particles in the air can often be seen as a reddish-brown layer over many urban areas.

Two important nitrogen oxides are NO and NO2, which are commonly grouped together under the term NOx. NOx forms when fuel is burned at high temperatures, as in a combustion process. The primary anthropogenic sources of NOx are motor vehicles, electric utilities, and other industrial, commercial, and residential sources that burn fuels. NOx can also be formed naturally.

 

caption Smog layer over the Great Lakes. (Source: NASA)

 

NOx plays an important role in the formation of ground level ozone (photochemical smog), acid rain, and particulate matter.

Another nitrogen oxide, nitrous oxide (N2O), is a greenhouse gas. It accumulates in the atmosphere with other greenhouse gases causing a gradual rise in the Earth's temperature. This will lead to increased risks to human health, a rise in the sea level, and other adverse changes to plant and animal habitat.

Glossary

Citation

Kubiszewski, I. (2011). Nitrogen. Retrieved from http://www.eoearth.org/view/article/154862

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