The most common formula for elemental oxygen is O2. This molecule is the major naturally existing form of elemental oxygen and is also called dioxygen, diatomic oxygen, oxygen gas and molecular oxygen. The other natural form of elemental oxygen is O3, an unstable molecule known as ozone.
Oxygen is the third most abundant element in the universe and the most abundant element on Earth.
- The oceans are 86 percent oxygen by weight.
- The crust is 47 percent oxygen by weight.
- The atmosphere is 21 percent oxygen by volume.
Properties of diatomic oxygen include:
- Reacts with diatomic hydrogen to form water
- Reacts vigorously with Group 1 metals (alkaline metals) to oxidize them
- Produces ozone when exposed to sparks, such as lightning
- Required for combustion and for metabolism of nutrients in animals
- Has three stable isotopes