Nitrogen
Nitrogen is the first element in Group 15 of the periodic table. The elements that make up this group are sometimes known as the nitrogen family, after nitrogen itself. Nitrogen has an atomic number of 7, an atomic mass of 14.0067, and a chemical symbol of N.
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[edit] Properties
Nitrogen is a colorless, odorless, tasteless gas with a density of 1.25046 grams per liter, slightly less than that of air (density = 1.29 grams per liter). Nitrogen has a boiling point of -320.42°F (-195.79°C) and a freezing point of -346.02°F (-210.01°C). When it freezes, nitrogen becomes a white solid that looks somewhat like snow. Nitrogen is slightly soluble in water, to the extent of about two liters of nitrogen to 100 liters of water.
Nitrogen is a relatively inactive element, evidenced by the fact that free nitrogen is abundant in the atmosphere. Nitrogen does combine with oxygen in the presence of lightning or a spark, the product of the reaction being nitric oxide: N2 + O2 --electrical energy 2NO. This reaction occurs commonly in the atmosphere and is the mechanism by which elemental nitrogen is converted to a compound. It is the first step in the process by which nitrogen is made available to plants and animals, where it is used primarily in the formation of amino acids and proteins. The conversion of elemental nitrogen to compounds of nitrogen is known as "nitrogen fixation."
[edit] Occurrence and Extraction
Nitrogen is the most abundant gas in the atmosphere, where it makes up 78.084% of the air we breathe. The element is also present in the Earth's crust, primarily in the form of nitrates and nitrites. Nitrogen is produced commercially by the fractional distillation of liquid air. Air is first cooled to the point at which all of the gases in it liquefy (close to -328°F/-200°C). The liquid air is then allowed to evaporate slowly. The first major gas to escape from liquid air as it warms is nitrogen. The nitrogen is captured and stored in steel cylinders for later transportation and use. Large amounts of nitrogen are made by this process. Typically, more than a trillion cubic feet of the element are produced in the United States alone each year, making it the second most important industrial chemical after sulfuric acid.
[edit] Uses
The most important use of nitrogen as an element is in situations where an inert gas is needed. For example, librarians often wish to store books and other precious documents where they will be protected from oxygen in the air (which would cause them to deteriorate). They may use sealed cases filled with nitrogen gas for such purposes. Nitrogen does not react with and damage the documents, as would oxygen. A similar application is the common incandescent light bulb, which may be filled with nitrogen, argon, or some other inert gas. The inert gas prevents the wire filament inside the bulb from reacting chemically with oxygen and burning out quickly.
Liquid nitrogen is also used very widely in situations where very cold temperatures are required. For example, it is used to quick dry foods, the first step in preserving them as frozen foods. Liquid nitrogen is also used by physicians to freeze and kill small tumors and other damaged tissue. After being frozen, the tumors or damaged tissue simply fall off, leaving healthy tissue behind.
Nitrogen is also the starting point for the manufacture of dozens of very important compounds. The most important of these compounds by far is ammonia (NH3). The discovery of a method by which nitrogen can be artificially "fixed" by German chemist Fritz Haber (1868-1934) in 1905 was one of the great milestones in the history of chemistry. Haber found that the two elements could be made to combine under high pressure and temperature in the presence of an appropriate catalyst. Ammonia gas is annually one of the top five chemicals in terms of production in the United States. Its most important use is in the manufacture of synthetic fertilizers, although very large amounts are also used to make nitric acid (HNO3), ammonium sulfate [(NH4)2SO4], and ammonium nitrate (NH4NO3). These compounds are also used to make fertilizers as well as explosives, fireworks, insecticides and herbicides, and rocket fuels. Ammonium sulfate is also used in water and sewage treatment systems, as a food additive, in the tanning of leather, and in fireproofing materials.
[edit] Health Issues
Nitrogen is absolutely essential to all living organisms. It is an essential element from which all amino acids and all proteins are made. Nitrogen is also an important component of nucleic acids, the chemicals in cells that carry genetic information and that direct the biochemical operations of all cells.
