Element 8 · Reactive nonmetal
Oxygen (O) — Element 8
Greek oxys genes — acid-forming
Oxygen (O) is a reactive nonmetal in Period 2, Group 16 of the periodic table with atomic number 8, standard atomic weight 15.999 u, and ground-state electron configuration [He] 2s² 2p⁴. At standard temperature and pressure it is classified as a gas with 6 valence electrons and common oxidation states -2.
Respiration, steelmaking, water
What are the atomic properties and physical constants of Oxygen?
Reference constants compiled from IUPAC standard atomic weights, the NIST Atomic Spectra Database, and the CRC Handbook.
- Atomic number (Z)
- 8
- Standard atomic mass
- 15.999 u
- Chemical family
- Reactive nonmetal
- Ground-state configuration
- [He] 2s² 2p⁴
- Electrons per shell
- 2, 6
- Valence electrons
- 6
- Common ion charges / oxidation states
- -2
- Phase at STP
- Gas
- Pauling electronegativity
- 3.44 Pauling
- First ionization energy
- 1,314 kJ/mol
- Atomic radius
- 48 pm
- Melting point
- -218 °C
- Boiling point
- -183 °C
- Discovery year
- 1774
- Table coordinate
- Period 2, Group 16
- Radioactivity
- Has stable isotope(s)
How are electrons arranged across Oxygen’s shells?
A neutral Oxygen atom contains 8 electrons distributed across 2 occupied principal energy shells ([He] 2s² 2p⁴). The table below compares Oxygen’s shell occupancy against each shell’s theoretical 2n² capacity.
| Principal Shell (n) | Spectroscopic Letter | Electrons in O | Max Shell Capacity (2n²) |
|---|---|---|---|
| n = 1 | K | 2 e⁻ | 2 e⁻ |
| n = 2 | L | 6 e⁻ | 8 e⁻ |
Frequently Asked Questions about Oxygen (O)
What is the atomic mass and atomic number of Oxygen (O)?
Oxygen (O) has atomic number Z = 8 (8 protons in its nucleus) and an IUPAC standard atomic weight of 15.999 u. It sits in Period 2, Group 16 and is classified as a reactive nonmetal.
What is the ground-state electron configuration of Oxygen?
The neutral ground-state electron configuration of Oxygen (Z = 8) is [He] 2s² 2p⁴. Across its 2 occupied principal shells (n = 1 to n = 2), the electrons per shell are 2, 6, with 6 valence electrons participating in bonding.
What are the common ion charges and electronegativity of Oxygen?
Oxygen commonly forms -2 oxidation states or ion charges in compounds. Its Pauling electronegativity is 3.44 and its first ionization energy is 1,314 kJ/mol.
When was Oxygen discovered and what is it used for?
Oxygen was discovered in 1774 (Greek oxys genes — acid-forming). Respiration, steelmaking, water
How does Oxygen compare to neighboring elements?
Other reactive nonmetal elements: