Quick answerOxygen (O) is a nonmetal with atomic number 8 and an atomic mass of 15.999 (2023), in group 16, period 2. It was discovered by Joseph Priestley in 1774. It is used for medical oxygen therapy and steel production. Its electron configuration is [He] 2s2 2p4.
Oxygen is the gas that keeps you alive with every breath, making up a fifth of the air and nearly half the mass of Earth's crust. Hospitals pipe it to patients who struggle to breathe, steelworks blast it through molten iron to burn off impurities, and rockets carry it as a liquid to burn fuel in space. It is also the element behind rust, fire, and the ozone layer that shields us from the Sun.
Key facts
| Symbol | O |
|---|---|
| Atomic number | 8 |
| Atomic mass | 15.999 (IUPAC standard atomic weight, 2023) |
| Category | nonmetal |
| Group | 16 |
| Period | 2 |
| Block | p-block |
| Electron configuration | [He] 2s2 2p4 |
| Discovered | Joseph Priestley, 1774 |
| Uses | medical oxygen therapy, steel production, liquid oxygen rocket propellant, welding and cutting, water treatment |
Overview
Oxygen is the element that keeps you alive with every breath. It has atomic number 8, an atomic mass of 15.999, and the electron configuration [He] 2s2 2p4, and it sits in group 16, period 2 of the periodic table. Joseph Priestley isolated it in 1774, and Antoine Lavoisier soon recognised it as the gas that makes things burn and animals breathe. Oxygen makes up about a fifth of the air, and it is the most abundant element in Earth's crust by mass, bound up in rocks, sand and water. Almost every living thing depends on it: cells burn food with oxygen to release energy, and plants and algae release it as a by-product of photosynthesis. Hospitals pipe oxygen to patients who struggle to breathe, and steelworks blast pure oxygen through molten iron to burn off carbon and other impurities. Rockets carry liquid oxygen to burn fuel where there is no air, welders use it to cut and join metal, and water treatment plants use it to clean drinking water. Oxygen is also behind rust, fire and decay, and high in the atmosphere it forms ozone, the layer that shields life from the Sun's ultraviolet light.
Frequently asked questions
What is oxygen used for?
Oxygen is used in hospitals to help patients who struggle to breathe, and in steelmaking, where it is blasted through molten iron to burn off impurities. Rockets carry liquid oxygen to burn fuel in space, welders use it to cut metal, and water plants use it to treat drinking water. It is also used in diving and aviation.
What is the symbol for oxygen?
The chemical symbol for oxygen is O, from its name, which comes from the Greek for acid-former. It has atomic number 8 and a standard atomic mass of 15.999, and it sits in group 16 and period 2 of the periodic table. Joseph Priestley isolated it in 1774, and it makes up about a fifth of the air.
What is the atomic number of oxygen?
Oxygen has atomic number 8, so it is the eighth element in the periodic table. Its atom holds eight protons and eight electrons, and its standard atomic mass is 15.999. It is a nonmetal in group 16 and period 2, with the electron configuration [He] 2s2 2p4, and it makes up about a fifth of the air.
Is oxygen a gas?
Yes, oxygen is a gas at room temperature. It is colourless, odourless and tasteless, and it makes up about a fifth of the air you breathe. Cooled far below freezing it becomes a pale blue liquid, which rockets carry as an oxidiser. Liquid oxygen is also used in hospitals and industry where pure oxygen is needed.
Who discovered oxygen?
Joseph Priestley is usually credited with discovering oxygen in 1774, when he heated mercuric oxide and collected a gas that made candles burn brightly. Carl Wilhelm Scheele had observed the same gas earlier, in 1771, but did not publish his work until 1777. Antoine Lavoisier then recognised it as a distinct element and named it oxygen.
Quick quiz
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Keep exploring
- Periodic table — all 118 elements
- Hydrogen (H) — another nonmetal, atomic number 1
- Carbon (C) — another nonmetal, atomic number 6
- Nitrogen (N) — another nonmetal, atomic number 7
- Phosphorus (P) — another nonmetal, atomic number 15
- Sulfur (S) — another nonmetal, atomic number 16
- Selenium (Se) — another nonmetal, atomic number 34
Sources & last updated
- CIAAW — Standard Atomic Weights
- PubChem Periodic Table
- Wikipedia — Timeline of chemical element discoveries
Last updated: . Figures are shown with their year; where sources disagree, the value is left out rather than estimated.