Math Is Fun Forum

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 51,538

Nitrogen

Nitrogen

Gist

Nitrogen is a chemical element with the symbol N and atomic number 7. It is a colorless, odorless, and tasteless gas that makes up about 78% of Earth's atmosphere. Nitrogen is a nonmetal and the lightest member of group 15 on the periodic table. It's essential for life, being a key component of amino acids, proteins, and nucleic acids.

Summary

Nitrogen is a chemical element; it has symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh in total abundance in the Milky Way and the Solar System. At standard temperature and pressure, two atoms of the element bond to form N2, a colourless and odourless diatomic gas. N2 forms about 78% of Earth's atmosphere, making it the most abundant chemical species in air. Because of the volatility of nitrogen compounds, nitrogen is relatively rare in the solid parts of the Earth.

It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772 and independently by Carl Wilhelm Scheele and Henry Cavendish at about the same time. The name nitrogène was suggested by French chemist Jean-Antoine-Claude Chaptal in 1790 when it was found that nitrogen was present in nitric acid and nitrates. Antoine Lavoisier suggested instead the name azote, from the Ancient Greek: "no life", as it is an asphyxiant gas; this name is used in a number of languages, and appears in the English names of some nitrogen compounds such as hydrazine, azides and azo compounds.

Elemental nitrogen is usually produced from air by pressure swing adsorption technology. About 2/3 of commercially produced elemental nitrogen is used as an inert (oxygen-free) gas for commercial uses such as food packaging, and much of the rest is used as liquid nitrogen in cryogenic applications. Many industrially important compounds, such as ammonia, nitric acid, organic nitrates (propellants and explosives), and cyanides, contain nitrogen. The extremely strong triple bond in elemental nitrogen,  the second strongest bond in any diatomic molecule after carbon monoxide (CO), dominates nitrogen chemistry. This causes difficulty for both organisms and industry in converting N2 into useful compounds, but at the same time it means that burning, exploding, or decomposing nitrogen compounds to form nitrogen gas releases large amounts of often useful energy. Synthetically produced ammonia and nitrates are key industrial fertilisers, and fertiliser nitrates are key pollutants in the eutrophication of water systems. Apart from its use in fertilisers and energy stores, nitrogen is a constituent of organic compounds as diverse as aramids used in high-strength fabric and cyanoacrylate used in superglue.

Nitrogen occurs in all organisms, primarily in amino acids (and thus proteins), in the nucleic acids (DNA and RNA) and in the energy transfer molecule adenosine triphosphate. The human body contains about 3% nitrogen by mass, the fourth most abundant element in the body after oxygen, carbon, and hydrogen. The nitrogen cycle describes the movement of the element from the air, into the biosphere and organic compounds, then back into the atmosphere. Nitrogen is a constituent of every major pharmacological drug class, including antibiotics. Many drugs are mimics or prodrugs of natural nitrogen-containing signal molecules: for example, the organic nitrates nitroglycerin and nitroprusside control blood pressure by metabolising into nitric oxide. Many notable nitrogen-containing drugs, such as the natural caffeine and morphine or the synthetic amphetamines, act on receptors of animal neurotransmitters.

Details

Nitrogen (N), nonmetallic element of Group 15 [Va] of the periodic table. It is a colourless, odourless, tasteless gas that is the most plentiful element in Earth’s atmosphere and is a constituent of all living matter.

Element Properties

atomic number  :  7
atomic weight  :  14.0067
melting point  :  −209.86 °C (−345.8 °F)
boiling point  :  −195.8 °C (−320.4 °F)
density (1 atm, 0° C)  :  1.2506 grams/litre
usual oxidation states      :  −3, +3, +5

Commercial production and uses

Commercial production of nitrogen is largely by fractional distillation of liquefied air. The boiling temperature of nitrogen is −195.8 °C (−320.4 °F), about 13 °C (−23 °F) below that of oxygen, which is therefore left behind. Nitrogen can also be produced on a large scale by burning carbon or hydrocarbons in air and separating the resulting carbon dioxide and water from the residual nitrogen. On a small scale, pure nitrogen is made by heating barium azide, Ba(N3)2. Various laboratory reactions that yield nitrogen include heating ammonium nitrite (NH4NO2) solutions, oxidation of ammonia by bromine water, and oxidation of ammonia by hot cupric oxide.

Elemental nitrogen can be used as an inert atmosphere for reactions requiring the exclusion of oxygen and moisture. In the liquid state, nitrogen has valuable cryogenic applications; except for the gases hydrogen, methane, carbon monoxide, fluorine, and oxygen, practically all chemical substances have negligible vapour pressures at the boiling point of nitrogen and exist, therefore, as crystalline solids at that temperature.

In the chemical industry, nitrogen is used as a preventive of oxidation or other deterioration of a product, as an inert diluent of a reactive gas, as a carrier to remove heat or chemicals and as an inhibitor of fire or explosions. In the food industry nitrogen gas is employed to prevent spoilage through oxidation, mold, or insects, and liquid nitrogen is used for freeze drying and for refrigeration systems. In the electrical industry nitrogen is used to prevent oxidation and other chemical reactions, to pressurize cable jackets, and to shield motors. Nitrogen finds application in the metals industry in welding, soldering, and brazing, where it helps prevent oxidation, carburization, and decarburization. As a nonreactive gas, nitrogen is employed to make foamed—or expanded—rubber, plastics, and elastomers, to serve as a propellant gas for aerosol cans, and to pressurize liquid propellants for reaction jets. In medicine rapid freezing with liquid nitrogen may be used to preserve blood, bone marrow, tissue, bacteria, and semen. Liquid nitrogen has also proven useful in cryogenic research.

Properties and reaction

Nitrogen is a colourless, odourless gas, which condenses at −195.8 °C to a colourless, mobile liquid. The element exists as N2 molecules, represented as :N:::N:, for which the bond energy of 226 kilocalories per mole is exceeded only by that of carbon monoxide, 256 kilocalories per mole. Because of this high bond energy the activation energy for reaction of molecular nitrogen is usually very high, causing nitrogen to be relatively inert to most reagents under ordinary conditions. Furthermore, the high stability of the nitrogen molecule contributes significantly to the thermodynamic instability of many nitrogen compounds, in which the bonds, although reasonably strong, are far less so than those in molecular nitrogen. For these reasons, elemental nitrogen appears to conceal quite effectively the truly reactive nature of its individual atoms.

A relatively recent and unexpected discovery is that nitrogen molecules are able to serve as ligands in complex coordination compounds. The observation that certain solutions of ruthenium complexes can absorb atmospheric nitrogen has led to hope that one day a simpler and better method of nitrogen fixation may be found.

Analytical chemistry

Often the percentage of nitrogen in gas mixtures can be determined by measuring the volume after all other components have been absorbed by chemical reagents. Decomposition of nitrates by sulfuric acid in the presence of mercury liberates nitric oxide, which can be measured as a gas. Nitrogen is released from organic compounds when they are burned over copper oxide, and the free nitrogen can be measured as a gas after other combustion products have been absorbed. The well-known Kjeldahl method for determining the nitrogen content of organic compounds involves digestion of the compound with concentrated sulfuric acid (optionally containing mercury, or its oxide, and various salts, depending on the nature of the nitrogen compound). In this way, the nitrogen present is converted to ammonium sulfate. Addition of an excess of sodium hydroxide releases free ammonia, which is collected in standard acid; the amount of residual acid, which has not reacted with ammonia, is then determined by titration.

Additional Information:

Appearance

A colourless, odourless gas.

Uses

Nitrogen is important to the chemical industry. It is used to make fertilisers, nitric acid, nylon, dyes and explosives. To make these products, nitrogen must first be reacted with hydrogen to produce ammonia. This is done by the Haber process. 150 million tonnes of ammonia are produced in this way every year.

Nitrogen gas is also used to provide an unreactive atmosphere. It is used in this way to preserve foods, and in the electronics industry during the production of transistors and diodes. Large quantities of nitrogen are used in annealing stainless steel and other steel mill products. Annealing is a heat treatment that makes steel easier to work.

Liquid nitrogen is often used as a refrigerant. It is used for storing sperm, eggs and other cells for medical research and reproductive technology. It is also used to rapidly freeze foods, helping them to maintain moisture, colour, flavour and texture.

Biological role

Nitrogen is cycled naturally by living organisms through the ‘nitrogen cycle’. It is taken up by green plants and algae as nitrates, and used to build up the bases needed to construct DNA, RNA and all amino acids. Amino acids are the building blocks of proteins.

Animals obtain their nitrogen by consuming other living things. They digest the proteins and DNA into their constituent bases and amino acids, reforming them for their own use.

Microbes in the soil convert the nitrogen compounds back to nitrates for the plants to re-use. The nitrate supply is also replenished by nitrogen-fixing bacteria that ‘fix’ nitrogen directly from the atmosphere.

Crop yields can be greatly increased by adding chemical fertilisers to the soil, manufactured from ammonia. If used carelessly the fertiliser can leach out of the soil into rivers and lakes, causing algae to grow rapidly. This can block out light preventing photosynthesis. The dissolved oxygen soon gets used up and the river or lake dies.

Natural abundance

Nitrogen makes up 78% of the air, by volume. It is obtained by the distillation of liquid air. Around 45 million tonnes are extracted each year. It is found, as compounds, in all living things and hence also in coal and other fossil fuels.

---

It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.