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Oxygen (O), element 8
Oxygen (O) is the chemical element with atomic number 8: a nonmetal in group 16, period 2. At 25 °C it is a gas, with an atomic mass of 16 u. Electronegativity of 3.44 on the Pauling scale: few atoms pull electrons harder.
Physical and chemical data
| Atomic number | 8 |
|---|---|
| Symbol | O |
| Atomic mass | 16 u |
| Density | 0.001429 g/cm³ |
| Melting point | -218.79 °C (54.36 K) |
| Boiling point | -182.95 °C (90.2 K) |
| Electronegativity (Pauling) | 3.44 |
| Electron configuration | [He]2s2 2p4 |
| Atomic radius (van der Waals) | 152 pm |
| Oxidation states | -2 |
| Physical state at 25 °C | gas |
| Family | nonmetal |
| Group and period | 16 / 2 |
| Discoverer and year | Carl Wilhelm Scheele and Joseph Priestley (1774) |
The discovery record belongs to Carl Wilhelm Scheele and Joseph Priestley, in 1774.
Neighbours on the table
Horizontally, one proton less lands on Nitrogen (Z=7); one more lands on Fluorine (Z=9). Vertically, group 16 gathers relatives with similar behaviour: Sulfur, Selenium, Tellurium, Polonium.
The story behind the name
The name means acid maker, from the Greek oxys, and records a famous mistake: Lavoisier believed every acid contained the new gas, which is not true. The discovery itself is one of the great disputes in science: Scheele obtained it first, in Sweden, but published late; Priestley isolated it in 1774 by heating mercury oxide and told Lavoisier about it over dinner in Paris; and Lavoisier understood what both men had in their hands. The misnamed gas keeps nearly all complex life on the planet breathing.
Physical and chemical data: PubChem Periodic Table (NCBI, compiling NIST and IUPAC), public domain, snapshot of 2026-07-10. Temperatures converted from kelvin; historical notes cross checked against classic chemistry references.
Last updated: · Methodology and sources