Nitrogen

Although molecular nitrogen is relatively inert, it will combine with a number of other elements at high temperatures. When it reacts with metals such as aluminum, magnesium, lithium, calcium, barium, strontium, and titanium, the products are known as nitrides. Lithium nitride (Li₃N), for example, is used to provide nitrogen in a variety of metallurgical operations.

Nitrogen and oxygen combine (again, at high temperatures) directly and indirectly to form a series of compounds that include nitrous oxide (or dinitrogen monoxide; N₂O), nitric oxide (or nitrogen monoxide; NO), dinitrogen trioxide (or nitrous anhydride; N₂O₃), nitrogen dioxide (NO₂), and dinitrogen pentoxide (or nitric anhydride; N₂O₅). Nitrogen and the halogens also react with each other to form a series of very unstable, explosive compounds that include nitrogen trifluoride (NF₃), nitrogen trichloride (NCl₃), and nitrogen triiodide (NI₃).

The most common compounds of nitrogen are those in which the element demonstrates oxidation numbers of 3^-, 3⁺, or 5⁺. Ammonia (NH₃) and its compounds (ammonium compounds) are examples of the first of these, the nitrites (NO^- ₂ ) are examples of the 3⁺ oxidation state, and the nitrates (NO^- ₃ ) are examples of the 5⁺ oxidation state.

The process by which nitrogen is cycled through the environment, from plants to animals to the atmosphere and back to plants, is known as the nitrogen cycle. In that cycle, nitrogen gas in the atmosphere is converted ("fixed") to a combined form by the action of lightning, in which it is converted to an oxide of nitrogen, or by certain nitrogen-fixing bacteria in the soil, which change it into nitrates and nitrites. The combined nitrogen is then taken up by plants and used to form plant proteins.

Plant proteins are eaten by animals, who convert the proteins into animal proteins. When an animal dies, the proteins are returned to the soil, where denitrifying bacteria break down compounds of nitrogen and return nitrogen to the atmosphere in the form of an element.

Three compounds of nitrogen traditionally rank in the top 25 among those chemicals produced in the largest volume in the United States. They are ammonia (number five in 1988), nitric acid (number 12 in 1988), and ammonium nitrate (number 14 in 1988). All three of these compounds are extensively used in agriculture as synthetic fertilizers. More than 80% of the ammonia produced, for example, goes to the production of synthetic fertilizers.

In addition to its agricultural role, nitric acid is also an important raw material in the production of explosives. Trinitrotoluene (TNT), gunpowder, nitroglycerin, dynamite, and smokeless powder are all examples of the kind of explosives made from nitric acid. Slightly more than 5% of the nitric acid produced is also used in the synthesis of adipic acid and related compounds used in the manufacture of nylon.