Allotropes of oxygen

Oxygen, 8O
Liquid oxygen (O2 at below −183 °C)
Oxygen
AllotropesO2, O3 (ozone) and more (see Allotropes of oxygen)
Appearancegas: colorless
liquid and solid: pale blue
Standard atomic weight Ar°(O)
  • [15.99903, 15.99977]
  • 15.999±0.001 (abridged)
Oxygen in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
–
↑
O
↓
S
nitrogen ← oxygen → fluorine
Atomic number (Z)8
Groupgroup 16 (chalcogens)
Periodperiod 2
Block  p-block
Electron configuration[He] 2s2 2p4
Electrons per shell2, 6
Physical properties
Phase at STPgas
Melting point(O2) 54.36 K ​(−218.79 °C, ​−361.82 °F)
Boiling point(O2) 90.188 K ​(−182.962 °C, ​−297.332 °F)
Density (at STP)1.429 g/L
when liquid (at b.p.)1.141 g/cm3
Triple point54.361 K, ​0.1463 kPa
Critical point154.581 K, 5.043 MPa
Heat of fusion(O2) 0.444 kJ/mol
Heat of vaporization(O2) 6.82 kJ/mol
Molar heat capacity14.689 J/(mol·K) (O)
29.378 J/(mol·K) (O2)
Specific heat capacity918.12 J/(kg·K) (O)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K)       61 73 90
Atomic properties
Oxidation statescommon: −2
−1, 0, +1, +2
ElectronegativityPauling scale: 3.44
Ionization energies
  • 1st: 1313.9 kJ/mol
  • 2nd: 3388.3 kJ/mol
  • 3rd: 5300.5 kJ/mol
  • (more)
Covalent radius66±2 pm
Van der Waals radius152 pm
Spectral lines of oxygen
Other properties
Natural occurrenceprimordial
Crystal structure ​cubic (cP16)
Lattice constant
a = 678.28 pm (at t.p.)
Thermal conductivity26.58×10−3  W/(m⋅K)
Magnetic orderingparamagnetic
Molar magnetic susceptibility+3449.0×10−6 cm3/mol (293 K)
Speed of sound330 m/s (gas, at 27 °C)
CAS Number7782-44-7
History
Namingfrom the Greek ὀξύς (acid, literally 'sharp', from the taste of acids) and -γενής (producer)
DiscoveryMichael Sendivogius
Carl Wilhelm Scheele (1604, 1771)
Named byAntoine Lavoisier (1777)
Isotopes of oxygen
Main isotopes Decay
Isotope abun­dance half-life (t1/2) mode pro­duct
15O trace 122.27 s β+ 15N
16O 99.8% stable
17O 0.0384% stable
18O 0.205% stable

There are several known allotropes of oxygen. The most familiar is molecular oxygen (O2), present at significant levels in Earth's atmosphere and also known as dioxygen or triplet oxygen. Another is the highly reactive ozone (O3). Others are:

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