Oxygen (O)
Oxygen is element 8, a reactive nonmetal in period 2, group 16 of the periodic table. At room temperature it is a gas.
Electron configuration [He] 2s2 2p4
Electrons per shell 2, 6
Oxygen data
| Atomic number | 8 |
|---|---|
| Symbol | O |
| Atomic mass | 15.999 u |
| Category | Reactive nonmetal |
| Group | 16 |
| Period | 2 |
| Block | p |
| State at 25 °C | gas |
| Melting point | 55 K (-218.1 °C) |
| Boiling point | 90 K (-183.1 °C) |
| Density | 0.001429 g/cm³ (1.429 g/L) |
| Electronegativity (Pauling) | 3.44 |
| Atomic radius | 73 pm |
| 1st ionization energy | 1314 kJ/mol |
| Electron affinity | -141 kJ/mol |
| Oxidation states | -2, -1, +1, +2 |
| Common ion charge | 2− |
| Discovered | 1774 |
Orbital diagram
Each box is one orbital holding up to two electrons of opposite spin. Following Hund’s rule, electrons spread out singly across a subshell before pairing.
Work through oxygen’s configuration and its ions →
Where oxygen sits
Oxygen belongs to the reactive nonmetals. Its Pauling electronegativity of 3.44 puts it among the strongest electron-pullers on the table; see the electronegativity chart and periodic trends for context. To use its mass in a calculation, try the molar mass calculator.
Oxygen FAQ
What is the electron configuration of oxygen?
Oxygen (Z = 8) has the configuration 1s2 2s2 2p4. In noble-gas shorthand that is [He] 2s2 2p4.
How many valence electrons does oxygen have?
6 (outer shell (n = 2)).
What is the atomic mass of oxygen?
The standard atomic weight of oxygen is 15.999 u, so one mole weighs 15.999 g.
Is oxygen a metal?
No. Oxygen is a reactive nonmetal.
What is the charge of a oxygen ion?
Oxygen most commonly forms O2−.