- Nitrogen (N) is a nonmetal with atomic number 7, located in Group 15 of the periodic table, known as the pnictogens.
- It has five valence electrons, giving it a strong tendency to form covalent bonds and a wide range of compounds in oxidation states from –3 to +5.
- Its atomic structure consists of seven protons, typically seven neutrons, and seven electrons arranged in two shells (two in the inner shell and five in the outer shell).
- Nitrogen exists naturally as two stable isotopes: nitrogen-14 (¹⁴N), which constitutes about 99.63% of natural nitrogen, and nitrogen-15 (¹⁵N), making up the remaining 0.37%.
- Under standard conditions, nitrogen is a diatomic gas (N₂), colorless, odorless, and tasteless, making up about 78% of Earth’s atmosphere by volume.
- Nitrogen is one of the most abundant elements in the universe, produced in stars primarily through the carbon–nitrogen–oxygen (CNO) fusion cycle.
- On Earth, the atmosphere serves as the largest nitrogen reservoir, while significant amounts are also bound in soils, oceans, and living organisms. Despite its abundance, most organisms cannot directly utilize atmospheric N₂ because of its triple covalent bond, which is one of the strongest in chemistry. This bond makes N₂ highly stable and inert under normal conditions.
- Nitrogen becomes biologically available through nitrogen fixation, a process carried out by certain bacteria and archaea, as well as through lightning and industrial synthesis.
- The discovery of nitrogen as a distinct element is credited to Scottish physician Daniel Rutherford in 1772, who described it as “phlogisticated air” after finding it was the portion of air that did not support combustion or respiration. Around the same time, other scientists, including Carl Wilhelm Scheele and Joseph Priestley, independently studied the gas. The name “nitrogen” comes from the Greek words nitron (native soda) and genes (forming), a reference to its occurrence in nitrates.
- Nitrogen is essential for life, being a fundamental component of amino acids, proteins, nucleic acids (DNA and RNA), and many biomolecules. It cycles through the biosphere in a complex process known as the nitrogen cycle, involving nitrogen fixation, nitrification, assimilation, ammonification, and denitrification. Industrially, nitrogen is critical for producing ammonia (NH₃) via the Haber–Bosch process, which is used to manufacture fertilizers, explosives, and a range of chemicals. Large-scale nitrogen fixation has dramatically increased global agricultural productivity but also contributed to environmental issues such as eutrophication.
- In its liquid form, nitrogen (boiling point −195.79 °C) is widely used as a cryogenic coolant for preserving biological samples, freezing food, and conducting low-temperature experiments. Gaseous nitrogen is used to create inert atmospheres for chemical processing, to prevent oxidation in food packaging, and to pressurize aircraft tires. Nitrogen compounds have diverse properties: nitrates are oxidizing agents used in fertilizers and explosives; nitrites are used in food preservation; and nitrogen oxides (NOₓ) are air pollutants that contribute to smog and acid rain.
- While nitrogen gas itself is inert and non-toxic, certain nitrogen compounds can be hazardous. Ammonia is corrosive and irritating to respiratory tissues; nitrogen dioxide (NO₂) is a toxic brown gas that can cause lung damage; and nitrous oxide (N₂O), while used medically as an anesthetic, is also a potent greenhouse gas. These hazards require careful control of nitrogen chemistry in industrial and environmental contexts.
