Nitrogen (N)

Nitrogen (symbol N) is the chemical element with atomic number 7: a nonmetal, a gas at 0 °C, with an atomic mass of 14.007 u. Discovered in 1772 (Daniel Rutherford).

Nitrogen makes up 78% of the air we breathe, but in a form so stable (two tightly bonded atoms) that most living things cannot use it directly. Yet it is indispensable to proteins and DNA. For a century, the Haber-Bosch process has turned it into fertilizer that feeds a large share of humanity. As a liquid, it freezes things at −196 °C.

Key facts

Atomic number: 7
Symbol: N
French name: Azote
Atomic mass: 14.007 u
Molar mass: 14.007 g/mol
Family: Nonmetals
Position: period 2, group 15, p-block
State at 0 °C: Gas
Melting point: -210 °C
Boiling point: -195.8 °C
Density: 0.00125 g/cm³
Electronegativity (Pauling): 3.04
First ionization energy: 1,402 kJ/mol
Atomic radius: 65 pm
Electron configuration: [He] 2s² 2p³
Abundance in Earth's crust: 19 ppm (34th most abundant element)
Indicative price: 0.14 $/kg (order of magnitude)
Radioactive: no
Discovery: 1772, Daniel Rutherford

Origin of the name

From the Greek nitron (saltpeter) and genes: “saltpeter-former.” Its French name, azote, means “unfit for life.”

What does nitrogen look like?

A colorless, odorless, tasteless gas. Liquefied, it looks like water that is constantly boiling, at −196 °C.

Where is nitrogen found?

78% of the atmosphere by volume, its main reservoir. It is scarce in Earth's crust (about 20 ppm), found in a few nitrate deposits. It accounts for about 3% of the human body's mass.

Natural sources

Air (78%)
Nitratine (Chile saltpeter)
Niter (saltpeter)

How is nitrogen produced?

Nitrogen gas and liquid nitrogen are obtained by distilling liquefied air. For fertilizers, the Haber-Bosch process combines nitrogen from the air with hydrogen under high pressure to make about 180 million tonnes of ammonia a year, using nearly 2% of the world's energy.

Top producers

China
Russia
United States
India

What is nitrogen used for?

Nitrogen fertilizers (ammonia, urea, nitrates).
Protective atmosphere for packaged food.
Liquid nitrogen for cryogenics, sample storage and dermatology.
Explosives (TNT, nitroglycerin) and gunpowders.
Tire inflation and the electronics industry.

In everyday life

A puffed-up bag of chips (filled with nitrogen, not air)
Garden fertilizers
Freezing off warts
Airbags (inflated with nitrogen)

Role in living things

A required building block of amino acids, and therefore proteins, and of the bases of DNA. Only certain bacteria can “fix” nitrogen from the air, notably those living in root nodules of legumes (peas, clover, soybeans).

Hazards of nitrogen

Inert and non-toxic, but a leak in a confined space can push out oxygen and suffocate without warning. Breathed under pressure while diving, it causes nitrogen narcosis and decompression sickness. Excess nitrates from farming pollute waterways and trigger green algal blooms.

Cosmic origin

Dying stars: Made slowly in red giants (stars like the Sun at the end of their lives).
Supernovae: Forged in the cores of massive stars, then scattered when they explode.

History of nitrogen

Scottish chemist Daniel Rutherford isolated it in 1772 as “mephitic air,” which snuffed out candles and suffocated mice. Lavoisier named it “azote,” from the Greek for “lifeless,” still its name in French. The international name nitrogen comes from niter (saltpeter), hence the symbol N.

Did you know?

An estimated half of the nitrogen in your body has passed through a Haber-Bosch plant.
Fritz Haber, awarded the 1918 Nobel Prize for synthesizing ammonia, also led Germany's chemical weapons program in World War I.
A drop of liquid nitrogen on the floor skates around on a cushion of vapor without wetting it: this is the Leidenfrost effect.

Isotopes of nitrogen

Two stable isotopes, with nitrogen-14 by far the most common. Nitrogen-15 is a tracer for following fertilizer through soils and plants.

nitrogen-13: radioactive, half-life 9.97 min. As labeled ammonia, it images blood flow to the heart in PET scans.
nitrogen-14: 99.636% of natural nitrogen, stable
nitrogen-15: 0.364% of natural nitrogen, stable. Stable tracer in agronomy, ecology and protein NMR.
nitrogen-16: radioactive, half-life 7.13 s. Formed in reactor water, its gamma rays reveal leaks in steam generators.

Common compounds

Caffeine (C₈H₁₀N₄O₂) · Urea (CO(NH₂)₂) · Paracetamol (C₈H₉NO₂) · Chlorophyll a (C₅₅H₇₂MgN₄O₅) · Ammonia (NH₃) · Gallium nitride (GaN) · Ammonium nitrate (NH₄NO₃)

Related elements

Same family (nonmetals): Hydrogen (H), Carbon (C), Oxygen (O), Phosphorus (P), Sulfur (S), Selenium (Se).

Same column (group 15): Phosphorus (P), Arsenic (As), Antimony (Sb), Bismuth (Bi), Moscovium (Mc).