008Reactive nonmetal · Group 16 · Period 2
Oxygen
Oxygen (O) is element 8, a reactive nonmetal in the p-block — group 16, period 2. It is a gas at room temperature with 2 electron shells (2, 6) and an atomic mass of 15.999 u.
- Atomic mass
- 16.00 u
- Phase · STP
- gas
- Melting
- 54 K · -219 °C
- Boiling
- 90 K · -183 °C
- Electronegativity
- 3.44
- Density
- 1.429 g/cm³
Photograph — Staff Sgt. Nika Glover, U.S. Air Force, Public domain, via Wikimedia Commons
Emission spectrum
The visible light Oxygen emits when energised — its unique spectral fingerprint.
Identity
- Atomic number
- 8
- Standard atomic weight
- 16.00 u
- Category
- Reactive nonmetal
- Group
- 16 · Chalcogens
- Period
- 2
- Block
- p-block
- Oxidation states
- -2
Physical properties
- Melting point
- 54 K · -219 °C
- Boiling point
- 90 K · -183 °C
- Density
- 1.429 g/cm³
- Molar heat capacity
- —
- Atomic radius
- 152 pm
- Electron affinity
- 140.976 kJ/mol
Atomic structure
8protons
8neutrons
8electrons
6valence e⁻
- Noble-gas notation
- [He] 2s2 2p4
- Full configuration
- 1s2 2s2 2p4
- Electrons per shell
- 2, 6
Periodic trends
Where Oxygen ranks across all 118 elements.
Ionization energies
Energy to remove each successive electron (kJ/mol).
1.3k1
3.4k2
5.3k3
7.5k4
11.0k5
13.3k6
71.3k7
84.1k8
Successive ionization energies (kJ/mol, log scale).
Discovery
- Discovered
- 1774
- Discovered by
- Carl Wilhelm Scheele
- Named by
- Antoine Lavoisier
- Appearance
- —