An Oxygen molecule has chemical formula O2.
• O is a free oxygen atom and O2 is two oxygen atoms chemically bound to form an oxygen molecule.
• the difference between oxygen (O) and oxygen (O2) is that the former is an oxygen atom while the latter consists of two O atoms bound together, forming a molecule also called oxygen or chemical name dioxygen.
• Oxygen is Earth's most abundant element, and after hydrogen and helium, it is the third-most abundant element in the universe.
• At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2.
• Oxygen makes up almost half of the Earth's crust in the form of oxides.