Oxygen (O)

Colorless gas

Oxygen is the element we breathe, supporting combustion and forming most of Earth's crust by mass, and with two unpaired 2p electrons, oxygen is highly reactive and forms oxides with most elements. Ozone (O₃) in the stratosphere shields life from ultraviolet radiation.

Key metrics

Density0.001429g/cm³

Melting point54.36K

Boiling point90.19K

Electronegativity3.44Pauling

Discovery

1774discovered

Discovered by: Joseph Priestley
Reactivity profile: Strong Oxidizer
Reactivity: High
Bonding: Covalent

Electron configuration

\textcolor{#6b7280}{[He]}\; \textcolor{#ef4444}{2_{s}^{2}}\; \textcolor{#3b82f6}{2_{p}^{4}}

[He] 2s2 2p4

Wave function

\Psi_{\text{O}} \approx \frac{1}{\sqrt{8!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_8(\mathbf{r}_8) \right|

Probability density $|\Psi|^2$ across the O valence shell.

Crystal structure

Orthorhombic

Lattice constantsa 1.00 · b 1.30 · c 0.90

Cell anglesα = β = γ = 90°

Coordination number—

Atoms per cell—

Atomic packing factor0.60

Physical properties

Atomic radius: 48 pm
Ionization energy: 1314 kJ/mol
Electron affinity: 141 kJ/mol
Crystal structure: Orthorhombic

Oxidation states

-2

Acid/base

Neutral

Strongly acidicStrongly basic

State at 25 °CGas

54.36 K90.19 K298 K

Emission spectrum

4 transitions

380450500550600650700780

VioletBlueGreenYellowRed

533.0nmO IIGreen30%

615.8nmO IOrange40%

777.4nmO I (triplet)IR100%

844.6nmO IIR80%

Dominant line 777.4 nmRange 533–845 nmTransitions 4