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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.[1][2][3]



colorless gas; light blue liquid.
A glass bottle half-filled with a bluish bubbling liquid

Light reflection lines of oxygen
General properties
Name, symbol, number oxygen, O, 8
Pronunciation /ˈɒks[invalid input: 'ɨ']ən/ OK-si-jən
Element category nonmetal, chalcogen
Group, period, block 162, p
Standard atomic weight 15.999(1)g/mol
Electron configuration [He] 2s2 2p4
Electrons per shell 2, 6 (Image)
Physical properties
Phase gas
Density (0 °C, 101.325 kPa)
1.429 g/L
Liquid density at b.p. 1.141 g/cm3
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/mol
Heat of vaporization (O2) 6.82 kJ/mol
Specific heat capacity (25 °C) (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 2, 1, −1, −2
Electronegativity 3.44 (Pauling scale)
Ionization energies
1st: 1313.9 kJ/mol
2nd: 3388.3 kJ/mol
3rd: 5300.5 kJ/mol
Covalent radius 66±2 pm
Van der Waals radius 152 pm
Crystal structure cubic
Magnetic ordering paramagnetic
Thermal conductivity (300 K) 26.58x10-3  W/(m·K)
Speed of sound (gas, 27 °C) 330 m/s
CAS registry number 7782-44-7
Most stable isotopes
Main article: Isotopes of oxygen
iso NA 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


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.

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 from air by separating it from nitrogen. Oxygen can also be produced by electrolysis. In this process, electricity passes through water. As a result, the water molecules break and release oxygen and hydrogen gas.


  1. "Liquid Oxygen Page". 2003 [last update]. Retrieved 22 May 2012. Check date values in: |year= (help)
  2. "Oxygen Facts - Periodic Table of the Chemical Elements". Retrieved 22 May 2012. Text "year] " ignored (help)
  3. "Lox/LH2". 2011 [last update]. Retrieved 22 May 2012. Check date values in: |year= (help)