Element: Oxygen
General data
| Element name | Oxygen |
|---|---|
| Chemical symbol | O |
| Atomic number Z | 8 |
| Year discovered | 1774 |
| Standard state (25°C) | Gas |
| Category | Nonmetal |
| Block | p |
| Atomic mass | 15.999 |
| CPK color | #FF0D0D |
Physical properties
| Melting point | 54.36 K (-218.79 °C) |
|---|---|
| Boiling point | 90.2 K (-182.9 °C) |
| Density | 0.001429 g/cm³ |
Energy properties
| First ionization energy | 13.618 eV |
|---|---|
| Electron affinity | 1.461 eV |
Atomic structure
| Protons | 8 (Atomic number) |
|---|---|
| Neutrons (O-16, most abundant isotope) | 8 |
| Electrons | 8 |
| Electron configuration | [He] 2s² 2p⁴ |
| Oxidation states | -2 |
| Electronegativity (Pauling) | 3.44 |
| Atomic radius (van der Waals) | 152 pm |
Ionization energies - NIST ASD (8 states)
| State | Charge | Ioniz. energy (eV) | Type |
|---|---|---|---|
| O I | 0+ | 13.618055 ± 0.000007 | measured |
| O II | 1+ | 35.12112 ± 0.00006 | measured |
| O III | 2+ | 54.93554 ± 0.00012 | semi-empirical |
| O IV | 3+ | 77.4135 ± 0.00025 | measured |
| O V | 4+ | 113.899 ± 0.0005 | measured |
| O VI | 5+ | 138.1189 ± 0.0021 | semi-empirical |
| O VII | 6+ | 739.32697 ± 0.00015 | calculated |
| O VIII | 7+ | 871.4099138 ± 0.0000012 | calculated |
Value type as given by NIST ASD: measured - from evaluated experimental data; calculated - from ab initio calculations (mostly highly ionised atoms that have not been measured; for the simplest ones, e.g. H I, the calculation is more accurate than measurement); semi-empirical - from interpolation, extrapolation or another semi-empirical method.
Photos
Isotopes (17)
| A | N | Half-life | Decay |
|---|---|---|---|
| O-11 | 3 | unbound (resonance) | 2p |
| O-12 | 4 | unbound (resonance) | 2p |
| O-13 | 5 | 8.58 ms | EC/β⁺ |
| O-14 | 6 | 70.618 s | EC/β⁺ |
| O-15 | 7 | 122.27 s | EC/β⁺ |
| O-16 | 8 | stable | - |
| O-17 | 9 | stable | - |
| O-18 | 10 | stable | - |
| O-19 | 11 | 26.470 s | β⁻ |
| O-20 | 12 | 13.51 s | β⁻ |
| O-21 | 13 | 3.42 s | β⁻ |
| O-22 | 14 | 2.19 s | β⁻ |
| O-23 | 15 | 96 ms | β⁻ |
| O-24 | 16 | 72 ms | β⁻ |
| O-25 | 17 | unbound (resonance) | n |
| O-26 | 18 | 0.005 ns | 2n |
| O-28 | 20 | < 100 ns | 2n |
Data sources
- PubChem Periodic Table API - Retrieved on 29 June 2026 - licence: CC0
- IUPAC CIAAW - Abridged Standard Atomic Weights 2024 - Table version: 2024 - licence: Public domain
- NNDC Wallet Cards 2023 - Data as of 15 October 2024 - licence: Public domain
- NIST Atomic Spectra Database (ASD) - Retrieved on 29 June 2026 - licence: © U.S. Secretary of Commerce
- Images of Elements - Retrieved on 29 June 2026 - licence: CC BY 3.0