8OOxygen15.999 u
Oxygen (O)
Oxygen is a nonmetal with atomic number 8, in period 2 and group 16 of the periodic table. Its atomic mass is 15.999 u and its electron configuration is [He] 2s² 2p⁴. Gas at 25 °C.
Key facts
| Atomic number | 8 |
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| Atomic mass | 15.999 u |
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| Category | Nonmetal |
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| Period | 2 |
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| Group | 16 |
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| Block | p |
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| Electron configuration | [He] 2s² 2p⁴ |
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| Electrons per shell | 2, 6 |
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| Electronegativity (Pauling) | 3.44 |
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| Oxidation states | −2, −1, +1, +2common in bold |
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| State at 25 °C | Gas |
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| Melting point | 54.8 K−218.35 °C |
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| Boiling point | 90.2 K−182.95 °C |
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| Density | 1.429 g/L |
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Atomic properties
| First ionization energy | 13.618 eV |
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| Electron affinity | 141 kJ/mol |
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| Atomic radius | 152 pm |
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| Covalent radius | 66 pm |
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| Van der Waals radius | 152 pm |
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| Common ions | O²⁻ |
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| Protons, neutrons, electrons | 8, 8, 8 |
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Physical and thermal properties
| Molar volume | 17.36 cm³/mol |
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| Heat of fusion | 0.222 kJ/mol |
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| Heat of vaporization | 3.41 kJ/mol |
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| Specific heat | 919 J/(kg·K) |
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| Thermal conductivity | 0.02658 W/(m·K) |
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| Thermal expansion | --- |
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| Mohs hardness | --- |
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| Young’s modulus | --- |
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| Crystal structure | Base-centered monoclinic |
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| Magnetic type | Paramagnetic |
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Identification and history
| CAS number | 7782-44-7 |
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| Latin name | Oxygenium |
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| Discovered by | Carl Wilhelm Scheele · 1771 |
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| Named by | Antoine Lavoisier · 1777 |
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Natural isotopes
| Isotope | Mass (u) | Abundance |
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| 16O | 15.994915 | 99.757 % |
| 17O | 16.999132 | 0.03835 % |
| 18O | 17.99916 | 0.2045 % |
Data checked against PubChem (NIH), IUPAC, the NIST Atomic Spectra Database and the IAEA (NUBASE and AME), the same data you see in the app.
A dash (---) means there is no reliable published measurement. The app never makes one up.
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Periodic Table