oxygen has an atomic weight and number of 15.999 g.mol -1 and 8. At room temp it is a gas and the boiling point/ melting point is 183/219 degrees Celsius. Discovered by Carl Wilhelm Scheele in 1773 (or earlier) in Uppsala and Joseph Priestly in 1774 in Wiltshire. We use it to breathe and make fire and it is the 3rd most abundant in the universe. it's categorys are Nonmetal, chalcogens.