Nitrogen
Atomic Data
| Atomic Number | 7 |
| Symbol | N |
| Atomic Weight | 14.007 u |
| Density (STP) | 1.2506 g/L |
| Melting Point | −210.00 °C (63.15 K) |
| Boiling Point | −195.79 °C (77.36 K) |
| Electronegativity | 3.04 (Pauling) |
| Electron Config. | 1s² 2s² 2p³ |
| Oxidation States | +5, +4, +3, +2, +1, 0, −1, −2, −3 |
| Phase at STP | Gas |
| Category | Reactive nonmetal |
| Period / Group | 2 / 15 |
| CAS Number | 7727-37-9 |
Electron Configuration
1s2 2s2 2p3
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 3 | 7 |
| Total | 5 | 7 | ||
Isotopes of Nitrogen
Nitrogen has two stable isotopes: nitrogen-14 (99.636%) and nitrogen-15 (0.364%). Nitrogen-15 is used as a stable isotope tracer in biological and agricultural research to track the fate of nitrogen fertilisers in soil and plants, and to study protein metabolism.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Nitrogen-14 | ¹⁴N | 7 | 7 | 99.636% | Stable |
| Nitrogen-15 | ¹⁵N | 7 | 8 | 0.364% | Stable |
Abundance & Occurrence
Nitrogen is the most abundant element in Earth's atmosphere, making up 78.08% by volume as diatomic N2. In Earth's crust it is far less concentrated at about 19 ppm, occurring mainly in minerals such as saltpetre (potassium nitrate) and Chile saltpetre (sodium nitrate). In the universe, nitrogen is less abundant than its neighbours oxygen and carbon, but is still a significant element produced in stellar nucleosynthesis.
Earth's Atmosphere By Volume (%)
Human Body Composition By Mass (%)
Discovery & History
Safety & Handling
- Asphyxiation hazard: Nitrogen gas is colourless and odourless. At high concentrations (above ~85% in air) it displaces oxygen and causes rapid loss of consciousness and death with no warning sensation. Many confined-space fatalities involve nitrogen used for purging or blanketing pipelines and vessels.
- Liquid nitrogen — cryogenic burns: Liquid nitrogen at −196°C causes severe frostbite on contact with skin, eyes, or mucous membranes. Use thermally insulated gloves, face shields, and cryogenic-rated storage vessels at all times.
- Pressure hazard: Liquid nitrogen evaporates rapidly (1 litre of liquid produces ~700 litres of gas). Never seal liquid nitrogen in a closed container without a pressure-relief valve — it will explode.
- Nitrogen oxides (NOx): Nitric oxide (NO) and nitrogen dioxide (NO2) are toxic gases produced during combustion and industrial processes. NO2 causes severe respiratory damage at moderate concentrations and is a precursor to photochemical smog and acid rain.
- Nitrous oxide (N2O): Used as a medical anaesthetic and propellant, but is a potent greenhouse gas (298× the global warming potential of CO2 over 100 years) and a significant ozone-depleting substance when emitted from agricultural soils.
Nitrogen in the Real World
Real-World Uses
- Ammonia and fertiliser synthesis — The Haber-Bosch process converts atmospheric N2 and H2 into ammonia (NH3), the precursor to virtually all nitrogen fertilisers (urea, ammonium nitrate, ammonium sulfate). Global ammonia production exceeds 175 million tonnes annually, underpinning modern agricultural yields.
- Food packaging inert atmosphere — Nitrogen gas is used to flush oxygen from food packaging, significantly slowing oxidation, rancidity, and microbial growth. Modified atmosphere packaging (MAP) using nitrogen extends shelf life of crisps, nuts, fresh pasta, coffee, and many other foods without preservatives.
- Liquid nitrogen cryogenics — Liquid nitrogen is the standard affordable cryogen for biobanking (sperm, embryos, stem cells), cryotherapy for skin lesions and tumours, food quick-freezing, and cooling superconducting magnets. It is produced by fractional distillation of liquid air at large scale.
- Explosives production — Nitrogen is central to virtually all high explosives and propellants: TNT, nitroglycerin, RDX, and ammonium nitrate all derive their energy from nitrogen–oxygen bonds that release large amounts of energy and gas when rapidly decomposed.
- Electronics manufacturing — Ultra-high-purity nitrogen is used as a blanketing and purging gas in semiconductor fabrication, soldering (to prevent oxidation), and in the production of compound semiconductors. Its inertness makes it ideal for protecting reactive surfaces during high-temperature processing.
- Pharmaceutical and chemical synthesis — Nitrogen atmosphere gloveboxes protect moisture- and oxygen-sensitive chemical reactions. Liquid nitrogen cooling is used in pharmaceutical manufacturing for low-temperature crystallisation and for preserving biological samples in drug discovery.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
Why is nitrogen important for life?
Nitrogen is a constituent of all amino acids, which are the building blocks of proteins, and of the nucleotide bases that form DNA and RNA. Without nitrogen, no living organism can build proteins, replicate its genetic material, or carry out cellular metabolism. The global nitrogen cycle — including biological nitrogen fixation by bacteria, the Haber-Bosch industrial synthesis of ammonia, and denitrification — circulates this essential element through the biosphere.
What is the Haber-Bosch process?
The Haber-Bosch process is the industrial synthesis of ammonia by reacting atmospheric nitrogen with hydrogen over an iron catalyst at high temperature (400–500°C) and pressure (150–300 atm). Developed by Fritz Haber and Carl Bosch in the early 20th century, it now produces about 175 million tonnes of ammonia per year — the basis for most synthetic fertilisers. It is estimated to sustain roughly half the world's current population by enabling modern agricultural yields.
What is liquid nitrogen used for?
Liquid nitrogen (boiling point −195.79°C) is used as a cost-effective cryogenic coolant in a wide range of applications: storing biological samples and gametes in biobanks, cryotherapy for skin lesions, food freezing, superconductor cooling, and as a pressurised propellant in some prototype vehicles. It is produced in large quantities by fractional distillation of liquid air.
How was nitrogen discovered?
Nitrogen was discovered in 1772 by Scottish physician Daniel Rutherford, who showed that a component of air remaining after oxygen was removed neither supported combustion nor sustained animal life. He called it ‘noxious air.’ Antoine Lavoisier later recognised it as a distinct element and named it azote (from Greek, meaning ‘no life’); the name nitrogen (nitre-forming) was later preferred.
Why does nitrogen make up 78% of the atmosphere?
Nitrogen gas (N2) accumulated in Earth's early atmosphere through volcanic outgassing and biological denitrification. Because N2 is chemically very inert — the triple bond between its two atoms requires 945 kJ/mol to break — it does not react easily with other atmospheric or crustal materials and does not dissolve significantly in water. This stability allows it to persist in the atmosphere over geological timescales, whereas more reactive gases are consumed by chemical weathering.