Oxygen in the biosphere is essential in the processes of respiration and metabolism, the means by which animals derive the energy needed to sustain life. Furthermore, oxygen is the most abundant element at the surface of the Earth. In combined form it is found in ores, earths, rocks, and gemstones, as well as in all living organisms. Oxygen is a gaseous chemical element in Group VA of the periodic table. The chemical symbol for atomic oxygen is O, its atomic number is 8, and its atomic weight is 15.9994.
Diatomic oxygen is colorless, odorless, and tasteless.
It is generally believed that Scheele was the first to isolate oxygen, but that Priestley, who independently achieved the isolation of oxygen somewhat later, was the first to publicly announce his findings. Lavoisier held the mistaken idea that oxides, when dissolved in water, would form only acids. The most abundant isotope of oxygen, with mass 16, is thought to be formed in hydrogen-burning stars by the capture of a proton by the isotopes of nitrogen and fluorine, with the subsequent emission of, respectively, a gamma ray and an alpha particle. In helium-burning stars the isotope of carbon with mass 12 is thought to capture an alpha particle to form the isotope with mass 16 with the emission of a gamma ray. Most of the Earth's rocks and soils are principally silicates.