Nitrogen
[He] 2s² 2p³ · 2 · 5
Four fifths of the air we breathe is nitrogen. The triple bond in N₂ is so strong that the gas is nearly inert, and breaking it in industrial ammonia synthesis was one of the most consequential technical achievements of the twentieth century.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 7
- Atomic mass
- 14.007 а.е.м.
- Electron configuration
- [He] 2s² 2p³
- Electrons per shell
- 2 · 5
- Block
- p-block
- Group
- Pnictogens
- Period
- 2
- Electronegativity (Pauling)
- 3.04
- Electronegativity (Allen)
- 3.07
- Atomic radius
- 56 pm
- Covalent radius
- 71 pm
- Van der Waals radius
- 155 pm
- Ionisation energy 1
- 1 402.3 kJ/mol
- Ionisation energy 2
- 2 856 kJ/mol
- Ionisation energy 3
- 4 578.1 kJ/mol
- Ionisation energy 4
- 7 475 kJ/mol
- Ionisation energy 5
- 9 444.9 kJ/mol
- Electron affinity
- -6.8 kJ/mol
- Common oxidation states
- -3, +3, +5
- Oxidation states
- -3, -2, -1, +1, +2, +3, +4, +5
Physical properties
- State at 25 °C
- gas
- Density
- 0.00125 g/cm³
- Melting point
- 63.15 K · -210 °C
- Boiling point
- 77.36 K · -195.8 °C
- Speed of sound
- 333 m/s
Thermal properties
- Heat of fusion
- 0.72 kJ/mol
- Heat of vaporisation
- 5.56 kJ/mol
- Specific heat capacity
- 1.04 J/(g·K)
- Thermal conductivity
- 0.02583 W/(m·K)
Mechanical properties
- Young's modulus
- no data
- Shear modulus
- no data
- Bulk modulus
- no data
- Poisson ratio
- no data
- Mohs hardness
- no data
- Brinell hardness
- no data
Electrical and magnetic properties
- Electrical resistivity
- no data
- Magnetic ordering
- diamagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- hexagonal close-packed (hcp)
- Lattice constants
- a = 386.1 pm · c = 626.5 pm
Abundance
- In the crust
- 19 mg/kg
- In the ocean
- 0.5 mg/L
- In the universe
- 1·10⁶ mg/kg
- In the human body
- 26 000 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 14N | 99.636 % | stable | — |
| 15N | 0.364 % | stable | — |
The nitrogen-15 to nitrogen-14 ratio in tissue rises with each step up a food chain, which is how the diets of ancient people and animals are reconstructed.
Discovery
- Year of discovery
- 1772
- Discovered by
- Daniel Rutherford
- Where
- Scotland
- Origin of the name
- from Greek azoos (lifeless); the English name means nitre-forming
History
Daniel Rutherford produced "noxious air" in 1772 by stripping oxygen and carbon dioxide from air, and showed that a candle went out and a mouse died in it. The Russian name says exactly that: from the Greek for lifeless.
Where it occurs
78 % of the atmosphere by volume. The crust holds little — 19 mg/kg, mostly as nitrate salts in arid regions. In living matter nitrogen sits in every protein.
How it is produced
By cryogenic distillation of liquid air: nitrogen boils 13 degrees below oxygen, which is what lets them be separated. It is one of the largest-tonnage industrial processes on Earth.
Role in living things
Nitrogen is in amino acids, nucleotides and ATP. Animals cannot use N₂ and get their nitrogen from food; only bacteria fix it from air, including the nodule bacteria on legume roots.
Safety
Non-toxic, but dangerous as an oxygen displacer: nitrogen asphyxia gives no warning, because what alarms a human is excess CO₂, not a shortage of oxygen. Under water, dissolved nitrogen causes narcosis and the bends.
Uses
- Ammonia synthesis, and through it the nitrogen fertiliser that feeds roughly half of humanity
- Inert atmospheres in food packaging, electronics and chemical plant
- Liquid nitrogen as a coolant: cryopreservation, cryotherapy, detector cooling
- Nitric acid, the feedstock for explosives, dyes and polymers
- Tyre inflation and displacing oxygen from aircraft fuel tanks
Curiosities
- The Haber–Bosch process consumes about 1 % of the world's energy and makes over 150 million tonnes of ammonia a year.
- Liquid nitrogen boils at 77 K, which is −196 °C.
- The N≡N triple bond is among the strongest in chemistry: 945 kJ/mol.
- Nitrogen is 78 % of the air, yet the crust holds less of it than of the rare earth cerium.
- Aurorae glow partly from excited nitrogen molecules, which give the pink-violet fringe.