Oxygen (O)
Reactive nonmetal · p-block · period 2 · group 16
Colourless gas; pale blue as a liquid and solid.
Oxygen (symbol O) is chemical element number 8, a reactive nonmetal in group 16, period 2 of the periodic table. Its standard atomic weight is 15.999 and its electron configuration is [He] 2s2 2p4. At room temperature it is a gas. Most abundant element in the Earth's crust (about 46% by mass).
Properties
| Atomic number | 8 |
|---|---|
| Atomic mass | 15.999 |
| Category | Reactive nonmetal |
| Block | p-block |
| Group · Period | 16 · 2 |
| Electron configuration | [He] 2s2 2p4 |
| Electrons per shell | 2, 6 |
| State at 25 °C | gas |
| Melting point | 54.36 K |
| Boiling point | 90.2 K |
| Density | 1.429 g/L |
| Electronegativity (Pauling) | 3.44 |
| Radioactive | No |
| Origin | primordial |
| Discovered | 1774 · Priestley & Scheele |
Key facts about Oxygen
- Most abundant element in the Earth's crust (about 46% by mass).
- Needed for combustion and for aerobic respiration.
- Ozone (O3) in the upper atmosphere blocks harmful ultraviolet light.
- Liquid oxygen is pale blue and is attracted by a magnet.
What Oxygen is used for
Steelmaking, medical breathing support, rocket oxidiser, water treatment, welding.
Where it sits in the periodic table
Oxygen is in group 16, period 2, of the p-block. Its electron configuration [He] 2s2 2p4 means its outermost shell holds 6 electrons, which is what places it here and explains much of its chemistry. See Oxygen on the interactive table →
Oxygen — frequently asked questions
What is Oxygen used for?
Steelmaking, medical breathing support, rocket oxidiser, water treatment, welding.
Is Oxygen radioactive?
No. Oxygen has at least one stable isotope and is not radioactive.
What is the electron configuration of Oxygen?
Oxygen has the electron configuration [He] 2s2 2p4, which is 2, 6 electrons per shell.
What group and period is Oxygen in?
Oxygen is in group 16, period 2, in the p-block. Its outer shell holds 6 electrons.
Who discovered Oxygen?
Oxygen was discovered in 1774 by Priestley & Scheele.