A nonmetallic element that constitutes nearly four-fifths of the air by volume, occurring as a colorless, odorless, almost inert diatomic gas, N₂, in various minerals and in all proteins and used in a wide variety of applications, including manufacture of ammonia, nitric acid, TNT, and fertilizers, and as a cryogen. Atomic number 7; atomic weight 14.0067; melting point -210.00°C; boiling point -195.80°C; valence 2, 3, 4, 5. See Periodic Table.