Oxygen combines with compounds and other elements in oxidation reactions. Rust, hydrated iron oxide, is produced when iron oxidises in the presence of water. Combustion may occur when a substance combines rapidly with oxygen in the air. For example, hydrogen burns in oxygen to make water, and methane burns in oxygen to make water and carbon dioxide.
| Symbol: | O |
| Atomic number: | 8 |
| Relative atomic mass: | 16 |
| Electronic configuration: | 1s1 2s2 2p4 |
| Molecular formula: | O2 |
| Relative molcular mass: | 32 |
| Boiling point: | -183 °C |
| Key properties: | Reactive gas that supports combustion. |
| Some major uses: | Manufacturing steel, cutting metals, producing medical breathing mixtures, supporting aquatic life in polluted rivers. |
| Discoverers: | Carl Wilhelm Scheele (1772), Joseph Priestley, Lavoisier (1774) |
All around us
Oxygen is the most plentiful element in the Earth's crust, and accounts for nearly half of it by mass (46.6%). Water is a compound of hydrogen and oxygen. Water is the most abundant compound on the Earth's surface and covers about two-thirds of it.
Without oxygen in the air, we would die of suffocation. When we breathe in, about one-fifth of the air rushing into our lungs is oxygen. The remainder is nearly all nitrogen and argon. The table and pie chart show the amounts of the three main gases in dry air.
