Oxygen (O) – element 8
Oxygen is a chemical element with the symbol O and atomic number 8. It is a reactive nonmetal in group 16 (chalcogens), period 2 of the periodic table (p-block), and is a gas at room temperature.
Oxygen (O) has atomic number 8, atomic mass 15.999 u and electron configuration [He] 2s2 2p4.
Oxygen facts
| Symbol | O |
|---|---|
| Atomic number | 8 |
| Atomic mass | 15.999 u (g/mol) |
| Category | reactive nonmetal |
| Group | group 16 (chalcogens) |
| Period | 2 |
| Block | p-block |
| Phase at 20 °C | Gas |
| Electron configuration | 1s2 2s2 2p4 |
| Noble-gas notation | [He] 2s2 2p4 |
| Electrons per shell | 2, 6 |
| Valence electrons | 6 |
Bohr model and shells
Oxygen has 8 electrons in 2 shells: 2, 6. Full configuration and noble-gas notation are in the table; work out any element or ion with the electron configuration calculator.
Physical and atomic properties
| Melting point | 54.36 K (-218.8 °C) |
|---|---|
| Boiling point | 90.188 K (-183.0 °C) |
| Density | 1.429 g/L |
| Electronegativity (Pauling) | 3.44 |
| Electron affinity | 140.976 kJ/mol |
| Ionization energies | 1313.9, 3388.3, 5300.5 kJ/mol (1st, 2nd, 3rd) |
| Discovered by | Carl Wilhelm Scheele |
Use the atomic mass in the molar mass calculator for any formula containing O.
Position in the periodic table
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Molecules with oxygen
- Acetic acid
- Acetone
- Adrenaline
- Alanine
- Aspirin
- ATP
- Caffeine
- Carbon dioxide
- Cholesterol
- Citric acid
- Cortisol
- Cytosine
Rotate each one in 3D, or draw your own structure in MolDraw.
Frequently asked questions
What is the atomic mass of oxygen?
The atomic mass of oxygen is 15.999 u, so one mole of oxygen atoms weighs 15.999 g.
What is the electron configuration of oxygen?
Oxygen has 8 electrons: 1s² 2s² 2p⁴, or [He] 2s² 2p⁴ in noble-gas notation. Electrons per shell: 2, 6.
How many valence electrons does oxygen have?
Oxygen has 6 valence electrons (group 16).
Is oxygen a metal?
No. Oxygen is a nonmetal (reactive nonmetal).
Where is oxygen on the periodic table?
Oxygen is in group 16 (chalcogens), period 2, in the p-block.
Data: Periodic-Table-JSON (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.