Nitrogen

Nitrogen is a chemical element with the symbol N and atomic number 7. It is the most abundant gas in Earth's atmosphere, making up about 78% by volume. In standard conditions it exists as a colorless, odorless diatomic molecule, N2, notable for a strong triple bond that renders it relatively inert.

N2's stability means nitrogen gas does not readily react with most substances at room temperature, though it can form compounds under high energy or with suitable catalysts. Its boiling point and melting point are well below room temperature, which makes liquid nitrogen useful for cooling and cryogenics.

Industrially, nitrogen is separated from air by fractional distillation. It is a key feedstock in the Haber-Bosch process to synthesize ammonia for fertilizers, and it is used to create inert atmospheres in metallurgy and the chemical industry to prevent unwanted reactions.

Biologically, nitrogen is essential for all living systems. It is a major component of amino acids, proteins, and nucleotides, supporting metabolism and genetic material. The nitrogen cycle involves fixation by bacteria and lightning, uptake by plants, mineralization, nitrification, and denitrification, cycling nitrogen through ecosystems.

Nitrogen has two stable isotopes, 14N and 15N. It can be a safety concern as an asphyxiant in confined spaces; nitrogen oxides are environmental pollutants produced by combustion. Common uses include fertilizers, inert atmospheres for industrial processes, and cryogenic applications.