Oxygen

nitrogen ← oxygen → fluorine - ↑ O ↓ S 8O Periodic table
Appearance
liquid oxygen with bubbles of oxygen gas 300px
General
Name, symbol, number	oxygen, O, 8
Element category	nonmetal, chalcogens
Group, period, block	16, 2, p
Standard atomic weight	15.9994(3) g/mol
Electron configuration	1s2 2s2 2p4
Electrons per shell	2, 6 (Image)
Physical properties
Density	(0 °C, 101.325 kPa) 1.429 g/L
Melting point	54.36 K, -218.79 °C, -361.82 °F
Boiling point	90.20 K, -182.95 °C, -297.31 °F
Critical point	154.59 K, 5.043 MPa
Heat of fusion	(O2) 0.444 kJ/mol1
Heat of vaporization	(O2) 6.82 kJ/mol1
Specific heat capacity	(25 °C) (O2) 29.378 J K−1 mol−1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k at T/K       61 73 90
Atomic properties
Oxidation states	2, 1, −1, −2 (neutral oxide)
Electronegativity	3.44 (Pauling scale)
Ionization energies (more)	1st: 1313.9 kJ·mol−1
	2nd: 3388.3 kJ·mol−1
	3rd: 5300.5 kJ·mol−1
Covalent radius	66±2 pm
Van der Waals radius	152 pm
Miscellaneous
Crystal structure	cubic
Magnetic ordering	paramagnetic
Thermal conductivity	(300 K) 26.58x10-3  W·m−1·K−1
Speed of sound	(gas, 27 °C) 330 m/s
CAS registry number	7782-44-7
EC number	231-956-9
Most stable isotopes
Main article: Isotopes of oxygen
iso N.A. half-life DM DE (MeV) DP 16O 99.76% 16O is stable with 8 neutrons 17O 0.039% 17O is stable with 9 neutrons 18O 0.201% 18O is stable with 10 neutrons
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Oxygen (ˈɒksɨdʒɨn) is a colourless gas which makes up about one fifth of the Earth's atmosphere. Its name comes from the Greek ὀξύς (oxys; acid, literally "sharp", from the taste of acids) and -γενής (-genēs; producer, literally "begetter").