Nitrogen (N2) (N₂) — Properties, Uses & Safety

Overview

Molecular nitrogen (N2) is a diatomic gas with a molar mass of 28.01 g/mol that makes up approximately 78% of Earth's atmosphere by volume, making it the most abundant gas in the air we breathe. It is a colorless, odorless, and largely inert gas at standard conditions. The remarkable stability of N2 comes from its triple bond (N≡N), one of the strongest bonds in chemistry with a bond dissociation energy of 945 kJ/mol. This triple bond consists of one sigma bond and two pi bonds, and its strength explains why nitrogen gas is so unreactive under normal conditions — breaking this bond requires enormous energy. Despite its atmospheric abundance, converting N2 into biologically useful forms (nitrogen fixation) is challenging. In nature, certain bacteria in the root nodules of legumes use the enzyme nitrogenase to fix atmospheric nitrogen into ammonia. Industrially, the Haber-Bosch process (N2 + 3 H2 → 2 NH3) accomplishes this at high temperatures (400–500 °C) and pressures (150–300 atm) using an iron catalyst — a reaction that revolutionized agriculture and now feeds roughly half the world's population through synthetic fertilizers. Liquid nitrogen, obtained by fractional distillation of liquid air, boils at −196 °C and is widely used in cryogenics, food flash-freezing, medical procedures (cryotherapy), and as a coolant for superconducting magnets. The GHS hazard code H280 (contains gas under pressure) applies to compressed nitrogen gas. For chemistry students, nitrogen connects an extraordinary range of topics: triple bonds and bond energy, molecular orbital theory, Lewis structures, the Haber-Bosch process (chemical equilibrium, Le Chatelier's principle, catalysis, and industrial chemistry), the nitrogen cycle in environmental science, and cryogenic properties of liquefied gases.

IUPAC Name

molecular nitrogen

CAS Number

7727-37-9

PubChem CID

947

Molecular Formula

N₂

Molar Mass

28.014 g/mol

State at STP

gas

Appearance

Colorless, odorless gas