Nitrogen is a chemical element with symbol N and atomic number 7. At room temperature, it is a colorless and odorless diatomic gas. Nitrogen is a common element in the universe, estimated at about seventh in total abundance in our galaxy and the Solar System. On Earth, the element forms about 78% of Earth's atmosphere and as such is the most abundant pure element. The element nitrogen was discovered as a separable component of air, by Scottish physician Daniel Rutherford, in 1772.