Nitrogen

Nitrogen is the chemical element with atomic number 7 and the symbol N. It is a colorless, odorless gas that makes up about 78 percent of Earth’s atmosphere by volume, and it is a building block of proteins and DNA. In the air it exists as pairs of atoms, N2, that are very unreactive, so industry and nature need special processes to convert it into forms that plants can use.

History of nitrogen

Compounds of nitrogen were known to alchemists, who made sal ammoniac, now called ammonium chloride, in Egypt by heating a mixture of dung, salt and urine. The gas itself was obtained in the 1760s by Henry Cavendish and Joseph Priestley, who removed the oxygen from air. They saw that the remaining gas extinguished a lit candle and that a mouse breathing it soon died, but neither concluded that it was a separate element.

The first person to propose that was a young student, Daniel Rutherford, in his doctoral thesis at Edinburgh in September 1772, and he is credited with the discovery. Carl Wilhelm Scheele and others were working on the same problem at the time. The name comes from the Greek words nitron, meaning native soda or nitre, and genes, meaning forming, because nitrogen is part of nitre, also known as saltpeter.

Rutherford removed oxygen and carbon dioxide from air and showed that the gas left behind would not support burning or breathing. Other scientists of the period, including Scheele, Cavendish and Priestley, described similar results with names such as burnt air or dephlogisticated air, which meant air without oxygen. The long list of near-discoverers is one reason the credit goes to the person who first called it a distinct substance.

Properties of nitrogen

Nitrogen has a standard atomic weight of about 14.007 and the electron configuration [He] 2s2 2p3. At room temperature it is a gas with a density of about 0.00125 grams per cubic centimeter. It condenses to a liquid at minus 195.8 degrees Celsius and freezes at minus 210.0 degrees Celsius.

The two atoms in a nitrogen molecule are joined by a triple bond, one of the strongest bonds in chemistry, which explains why nitrogen gas is so inert. It sits in group 15, sometimes called the pnictogens, and its common oxidation states range from minus 3 to plus 5. The wide range allows it to form ammonia, nitrates, nitrites and many organic compounds.

Occurrence and production of nitrogen

Nitrogen gas is 78.1 percent of Earth’s air by volume, and the atmosphere is estimated to hold about 4,000 trillion tons of it. By comparison, the atmosphere of Mars is only about 2.6 percent nitrogen. Nitrogen is also found in all living systems as part of biological compounds, and therefore in coal and other fossil fuels derived from living things.

Industry obtains nitrogen by cooling air until it liquefies and then separating the gases by fractional distillation, a process that uses their different boiling points. Around 45 million tonnes are extracted each year, according to the Royal Society of Chemistry.

PubChem lists a first ionization energy of 14.534 electronvolts for nitrogen, a van der Waals radius of 155 picometers and a covalent radius of about 71 picometers. The crust holds roughly 19 milligrams per kilogram, so most of the planet’s accessible nitrogen sits in the air above it rather than in rock.

Uses of nitrogen

The largest use of nitrogen is to make ammonia. In the Haber process, nitrogen is reacted with hydrogen, and about 150 million tonnes of ammonia are produced this way each year. Ammonia is the starting point for fertilizers, explosives and, by the Ostwald process, nitric acid. Nitrogen is also used to make nylon and dyes.

Nitrogen gas is used where an unreactive atmosphere is needed: to preserve foods, to protect materials in the electronics industry during the making of transistors and diodes, as a shield in welding and soldering, and in annealing stainless steel and other steel products. Oil companies use high-pressure nitrogen to help force crude oil to the surface.

Liquid nitrogen is an inexpensive cryogenic liquid. It is used for refrigeration, for storing cells such as sperm and eggs for medical research and reproductive technology, and to freeze foods quickly so that they keep their moisture, color and texture.

Among the strengths of liquid nitrogen is its low cost compared with other coolants, and the gas supplies a dry, oxygen-free environment that slows spoilage and prevents unwanted reactions in manufacturing. Because nitrogen is so widely available from air, it is among the cheapest industrial gases, even though fixing it into chemical form remains energy intensive.

Isotopes of nitrogen

Nitrogen has two stable isotopes, nitrogen-14 and nitrogen-15. IUPAC data give nitrogen-14 an abundance of about 99.636 percent and nitrogen-15 about 0.364 percent. The small proportion of nitrogen-15 makes it useful in research as a tracer, because scientists can follow nitrogen through chemical and biological systems by measuring shifts in this ratio.

The nitrogen cycle and environmental effects

Nitrogen cycles naturally through living organisms. Green plants and algae take it up as nitrates and use it to build the bases of DNA and RNA and all the amino acids, which are the building blocks of proteins. Animals obtain nitrogen by eating other living things. Soil microbes convert nitrogen compounds back to nitrates for reuse, and nitrogen-fixing bacteria supply more by pulling nitrogen directly from the air. Lightning also fixes some atmospheric nitrogen.

Fertilizers made from ammonia can raise crop yields greatly, but if used carelessly they can wash from soil into rivers and lakes. There they feed fast algae growth that blocks light, uses up dissolved oxygen and can kill the water body. Nitrogen gas itself is not toxic, but as with any gas that displaces air, it can cause suffocation in enclosed spaces.

Editorially reviewed by Specialty Digest Editorial TeamLast reviewed November 4, 2026Researched and drafted with AI assistanceReport an issue