Nitrogen

History

(L. nitrum, Gr. Nitron, native soda; and genes, forming) Nitrogen was discovered by chemist and physician 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, Cavendish, Priestley, and others. They called it “burnt" or" dephlogisticated air,” which meant air without oxygen.

Properties

The French chemist Antoine Laurent Lavoisier mistakenly named nitrogen azote, meaning without life. However, nitrogen compounds are found in foods, organic materials, fertilizers, poisons, and explosives. Nitrogen, as a gas is colorless, odorless, and generally considered an inert element. As a liquid (boiling point = minus 195.8^oC), it is also colorless and odorless, and is similar in appearance to water. Nitrogen gas can be prepared by heating a water solution of ammonium nitrite (NH₄NO₃).

The nitrogen cycle is one of the most important processes in nature for living organisms. Although nitrogen gas is relatively inert, bacteria in the soil are capable of “fixing” the nitrogen into a usable form (as a fertilizer) for plants. In other words, Nature has provided a method to produce nitrogen for plants to grow. Animals eat the plant material where the nitrogen has been incorporated into their system, primarily as protein. The cycle is completed when other bacteria convert the waste nitrogen compounds back to nitrogen gas. 

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. From an exhaustible source in our atmosphere, nitrogen gas can be obtained by liquefaction and fractional distillation. Nitrogen is found in all living systems as part of the makeup of biological compounds.

Uses

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, 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 is often used in cryogenics. Liquid nitrogen is produced by distillation from liquid air. At atmospheric presure, nitrogen condenses at -195.8 degrees Celsius. It is the liquid coolant frequently used for demonstrations in science education. 

Ammonia (NH₃) is the most important commercial compound of nitrogen. It is produced by the Haber Process. Natural gas (methane, CH₄) is reacted with steam to produce carbon dioxide and hydrogen gas (H₂) in a two step process. Hydrogen gas and nitrogen gas reacted via the Haber Process to produce ammonia. 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, used in the plastic industry, and used in the livestock industry as a feed supplement. Ammonia is often the starting compound for many other nitrogen compounds.

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 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.

Hazards

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.