Nitrogen

Nitrogen is a colourless, odourless gas that makes up 78% of the air you breathe. Without nitrogen there would be no food, because plants need it to grow. And without plants, there would be no animals, including us. It is also the key ingredient in explosives, from fireworks to modern weapons.

• Atomic Number77 protons, 7 electrons
• Atomic Mass14.007 uAbout 14× heavier than hydrogen
• State at Room TempGas78% of the air you breathe
• Density0.0012506 g/cm³Slightly lighter than air
• Melting / Boiling-210°C / -195.8°CLiquid nitrogen at −196°C
• Discovered1772Daniel Rutherford, 1772

What is nitrogen?

Nitrogen is a non-metal in Group 15 of the periodic table. At room temperature it exists as a diatomic molecule: two nitrogen atoms joined by a powerful triple bond (N₂). That triple bond is one of the strongest in chemistry, which is why nitrogen gas is so stable and unreactive under normal conditions. To break it apart and use nitrogen in chemical reactions requires enormous energy, extreme temperatures or specialised bacteria.

Nitrogen gets its name from the Greek words nitron (a mineral salt known in antiquity) and genes (maker). It was named this because nitrogen compounds, including potassium nitrate, known as saltpetre, were known long before the element itself was isolated. The symbol N comes directly from the name. Lavoisier called it azote (Greek for lifeless) because animals died in it, and this name is still used in some languages.

Where you find nitrogen

In space

Nitrogen is found in the Sun and in stars. Saturn's moon Titan has an atmosphere mostly made of nitrogen, similar to Earth's in composition, though far colder. Pluto is covered with nitrogen ice and has a thin nitrogen atmosphere.

On Earth

Nitrogen is everywhere, roughly four fifths of every breath you take is nitrogen. Despite this abundance, most living things cannot use it directly from the air. They need it in the form of compounds such as ammonia or nitrates.

• The atmosphere. Air is 78% nitrogen gas (N₂), a vast reservoir that most plants and animals cannot access directly.
• Soil nitrates. Certain bacteria in soil and on plant roots can "fix" nitrogen from the air, converting it into ammonia and nitrates that plants can absorb through their roots.
• Natural deposits. Sodium nitrate (Chilean saltpetre) occurs naturally in the Atacama Desert and was once a major source of nitrogen for fertilisers.

How we use nitrogen

• Fertilisers. More than half the food eaten by the world's population depends on nitrogen fertilisers made by the Haber-Bosch process, which combines nitrogen from the air with hydrogen to make ammonia, then converts it to fertilisers.
• Liquid nitrogen. At −196°C, nitrogen becomes a liquid that instantly freezes almost anything it touches. It preserves biological samples, freezes food, removes warts in medicine and creates spectacular vapour effects in cooking.
• Car airbags. When a car crashes, a chemical reaction produces a burst of nitrogen gas in less than a thirtieth of a second, inflating the airbag that cushions the driver and passengers.
• Food packaging. Nitrogen gas is pumped into crisp packets and food containers to keep oxygen out, preventing food from going stale or mouldy. Those puffy crisp bags are full of nitrogen, not air.

How it was discovered

Nitrogen was identified in 1772 by the Scottish physician Daniel Rutherford, who called it "noxious air" because animals placed in a jar of it quickly died. Several other scientists, Carl Wilhelm Scheele, Henry Cavendish and Joseph Black, were investigating the same substance at roughly the same time. It was Antoine Lavoisier who recognised it as a distinct element, naming it azote from the Greek for lifeless. The name nitrogen came later, from the compound nitre (potassium nitrate) in which it was a key ingredient.

Nitrogen is the invisible gas that holds life together, from the air in your lungs to the fertiliser in your food. Moving one step further along the periodic table brings you to oxygen, the gas that makes burning and breathing possible.