Nitrogen is a gaseous, non-metallic chemical element made of seven protons and seven electrons. In its most common stable form, nitrogen also has seven neutrons.
Nitrogen occurs as an odorless and colorless gas at Earth's surface. It constitutes the largest component of Earth's air, making up about 78 percent by volume. Nitrogen forms part of the biological compounds found in all living things. It is part of the nitrogen cycle, the process by which green plants convert nitrogen into substances they can use. Nitrogen becomes a liquid when it is cooled to about -320 degrees Fahrenheit and serves as a refrigerant in its liquid form. The scientist Daniel Rutherford discovered nitrogen in 1772.