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element with the atomic number of 8

Oxygen (O) is a chemical element. In nature, oxygen is a gas with no color or smell. Oxygen is a very important element because we need it to live. It is a part of the air people breathe and the water people drink. Many living things (including humans) need oxygen to live and breathe, though it is poisonous to some forms of life. In liquid state of matter, oxygen is light blue.[2][3][4]

Oxygen,  8O
A transparent beaker containing a light blue fluid with gas bubbles
Liquid oxygen boiling
General properties
AllotropesO2, O3 (Ozone)
Appearancegas: colorless
liquid: pale blue
Standard atomic weight (Ar, standard)[15.9990315.99977] conventional: 15.999
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


Atomic number (Z)8
Groupgroup 16 (chalcogens)
Periodperiod 2
Element category  reactive nonmetal
Electron configuration[He] 2s2 2p4
Electrons per shell
2, 6
Physical properties
Phase at STPgas
Melting point54.36 K ​(−218.79 °C, ​−361.82 °F)
Boiling point90.188 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 capacity(O2) 29.378 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K)       61 73 90
Atomic properties
Oxidation states−1, −2, +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
Color lines in a spectral range
Spectral lines of oxygen
Other properties
Natural occurrenceprimordial
Crystal structurecubic
Cubic crystal structure for oxygen
Speed of sound330 m/s (gas, at 27 °C)
Thermal conductivity26.58×10−3  W/(m·K)
Magnetic orderingparamagnetic
Magnetic susceptibility+3449.0·10−6 cm3/mol (293 K)[1]
CAS Number7782-44-7
DiscoveryCarl Wilhelm Scheele (1771)
Named byAntoine Lavoisier (1777)
Main isotopes of oxygen
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
16O 99.76% stable
17O 0.04% stable
18O 0.20% stable
| references


Discovery of oxygenEdit

Oxygen was initially discovered in 1772 by Carl Wilhelm Scheele. Then Joseph Priestley also discovered it two years later and spread the news before Scheele. This made many people think that Priestley discovered oxygen first. The word oxygen comes from Greek words: oxus (acid) and gennan (generate). Oxygen comes to earth from all parts of the universe in meteorites. It is also found in minerals and plants that grow on the earth and other planets.

Oxygen in natureEdit

A drop of water.

Water contains oxygen. When one oxygen atom combines with two hydrogen atoms, they form a molecule of water (also written as H2O). This water is required by all living things to live.

Oxygen molecules in the atmosphere combine to for diatomic molecules, O2.

Air also contains oxygen. Air is made of many gases that are mixed together. Approximately 21% of the air is oxygen. Oxygen is especially important because all animals use oxygen to get energy from their food.

Combustion of wood in a match.

Uses of oxygenEdit

Oxygen is what makes burning possible. This is called combustion. When an object or something burns, oxygen combines with another substance and releases heat and light. For instance, when wood burns, the oxygen in air combines with the wood to create fire. This ability of oxygen has many uses. But it also makes pure oxygen very dangerous. If pure oxygen touches a flame or spark, it can make a hot fire and cause great damage. Combustion is used in many ways.

  • When oxygen is mixed with acetylene, it can create a very hot flame. This is used in welding, of metals.
  • Liquid oxygen can make a hot flame with other propellants for rocket engines.
  • Oxygen can be used in smelting metal from ore.
  • Oxygen is used in hospitals for killing bacteria. It is also used when a patient has had carbon monoxide poisoning.
  • Oxygen is used in water treatment to purify the water to make it safe to drink.
  • People with certain illnesses are less sick when they breathe pure oxygen.

Production of gasEdit

Pure oxygen can be produced in several ways. In nature, plants produce oxygen by using sunlight, carbon dioxide (another gas) and water. This process is called photosynthesis. Most of the oxygen in the air is produced by photosynthesis.

People mostly get pure oxygen for industry by fractional distillation of air. Oxygen can also be produced by electrolysis of water. Airliners carry emergency oxygen generators that use sodium chlorate and other solid chemicals. Some small machines separate oxygen from air using special membrane filters.


  1. Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.
  2. "Liquid Oxygen Page". 2003 [last update]. Retrieved 22 May 2012. Check date values in: |year= (help)
  3. "Oxygen Facts - Periodic Table of the Chemical Elements". Retrieved 22 May 2012.
  4. "Lox/LH2". 2011 [last update]. Retrieved 22 May 2012. Check date values in: |year= (help)