The atomic mass of oxygen is 15.9994 atomic mass units. Oxygen has an atomic number of 8 and is classified as a non-metal. Its symbol is O.
Oxygen was discovered in 1774 by Joseph Priestly, according to Chemical Elements. Its name comes from the Greek words "oxus," which means acid, and "gennan," which means generate. Oxygen has a melting point of negative 218.4 degrees Celsius and a boiling point of negative 183 degrees Celsius. It has eight protons and eight neutrons, and it has six electrons in its outer shell. It is colorless and has a cubic structure when crystallized.