Nitrogen is a nonmetallic chemical element. It occurs in nature as a colorless, odorless, and tasteless gas. This gas makes up about 78 percent of the earth’s atmosphere by volume. Daniel Rutherford, a Scottish physician, discovered nitrogen in 1772.
The chemical symbol for nitrogen is N. Nitrogen gas consists of two nitrogen atoms bonded together to form a molecule. The gas may be condensed to a liquid that boils at –195.8 °C and freezes at –209.9 °C. Nitrogen gas does not combine easily with other elements. But nitrogen atoms are part of many chemical compounds. Nitrogen’s atomic number (number of protons in its nucleus) is 7. Its relative atomic mass is 14.0067. An element’s relative atomic mass equals its mass (amount of matter) divided by 1/12 of the mass of an atom of carbon 12, the most abundant form of carbon. For information on the position of nitrogen on the periodic table, see the article Periodic table.
Element, Chemical (table: Table of the elements)
Nitrogen and life
All organisms must have nitrogen to live. Nitrogen is part of all amino acids, the building blocks of proteins. Plants make all the amino acids they need. Animals produce only some of these compounds and must get the rest by eating other animals and plants.
Nitrogen is constantly being removed from the air and returned to it in a series of chemical reactions known as the nitrogen cycle. In the first part of this process, called nitrogen fixation, nitrogen gas is converted to nitrogen compounds that plants can use. Nitrogen in the air reacts with water to form nitric acid, which is deposited in the soil by rain. In addition, certain bacteria and yeasts change nitrogen from the air into compounds plants can use. Bacteria in swellings on the roots of legumes, such as peas and beans, can also do this.
In the next stage of the nitrogen cycle, plants use nitrogen compounds in the soil to make protein. Fertilizers increase the usable nitrogen in the soil. Plant proteins are then eaten by animals. In the final stage, the decay of animal wastes and of dead plants and animals returns nitrogen compounds to the soil and nitrogen gas to the atmosphere. See Nitrogen cycle.
Uses of nitrogen
Manufacturers obtain pure nitrogen by making liquid air. They then separate the nitrogen from the oxygen and other gases in air by the process of distillation (see Liquid air). During the process of distillation, the nitrogen is collected and stored under pressure in specially designed metal containers. Small amounts of nitrogen can be prepared by gently heating a water solution of ammonium nitrite.
Pure nitrogen gas is used as a “blanket” by certain industries to keep oxygen away from specific areas. For example, the food industry uses nitrogen to prevent oxygen from reaching such foods as fresh fruits and spoiling them. The food industry also uses liquid nitrogen to quick-freeze food and to refrigerate food during transport. Scientists use liquid nitrogen to produce the low temperatures needed in some experiments.
Production of nitrogen compounds.
The principal use of nitrogen is in the production of ammonia, a gas that consists of nitrogen and hydrogen. Manufacturers produce ammonia chiefly by the Haber process. In this process, nitrogen and hydrogen are combined at high temperatures and pressures (see Haber process). Ammonia is used as a fertilizer, as a refrigerant, and in the production of nitric acid and other chemicals. Household ammonia, which is a cleaning agent, consists of a dilute solution of ammonia gas in water. See Ammonia.
Nitric acid is a second major nitrogen compound produced by industry. It is made from ammonia in a series of reactions called the Ostwald process. Nitric acid is used mainly to make fertilizer (see Nitric acid). Nitrogen compounds are also important in drugs, dyes, explosives, poisons, and synthetic fibers.
Nitrogen in agriculture.
Almost all fertilizers contain nitrogen, which is necessary for the healthy growth of plants. Farmers may inject ammonia gas directly into the soil. Liquefied ammonia and such compounds as ammonium sulfate and ammonium nitrate also are used as nitrogen fertilizers. Other sources of nitrogen include nitrate compounds, manure, and guano, the waste material of sea birds. See Fertilizer.
Farmers can also supply nitrogen to their fields by rotating crops. In crop rotation, a farmer plants a field one year with corn, wheat, or some other crop that removes nitrogen from the soil. The next year, the farmer plants the field with legumes that restore nitrogen to the soil.
Nitrogen and pollution
People influence the nitrogen cycle. The use of nitrogen fertilizers adds nitrogen to the soil. Rain water carries unused fertilizer and other nitrogen compounds into streams and lakes, where the compounds cause water plants and algae to multiply. As the plants and algae die and decay, they use up oxygen, endangering animal life in the body of water.
Nitrogen oxides pollute the air. Pollutants are released by burning fossil fuels, such as coal and gasoline. Sunlight causes nitrogen oxides in the lower atmosphere to react with oxygen to form ozone, an irritating substance in smog. Nitrogen oxides can also return to earth as nitric acid, a major ingredient of acid rain.
Jet engines produce nitrogen oxides in the upper atmosphere, where the compound may harm the environment in a different way. Nitrogen oxides can promote the decomposition of ozone in the upper atmosphere. Here, ozone benefits animals and plants by shielding them from harmful ultraviolet light.
