Physics & Chemistry


May 10, 2011, 4:01 pm
Content Cover Image

Vial of glowing ultrapure oxygen, O2. Original size in cm: 1 x 5. Source:

Oxygen is the third most abundant element in the universe. It is a non-metallic element with the symbol O, the atomic number 8, an atomic weight of 15.999, and a melting point of about -218.4°C. Oxygen gas is colorless, odorless, and tasteless. The liquid and solid forms are a pale blue color and are strongly paramagnetic.

Previous Element: Nitrogen

Next Element: Fluorine


Physical Properties
Color colorless
Phase at Room Temp. gas
Density (g/cm3) 0.0014
Hardness (Mohs) ---
Melting Point (K) 54.8
Boiling Point (K) 90.2
Heat of Fusion (kJ/mol) 0.4
Heat of Vaporization (kJ/mol) ---
Heat of Atomization (kJ/mol) 249
Thermal Conductivity (J/m sec K) 0.03
Electrical Conductivity (1/mohm cm) 0
Source air
Atomic Properties
Electron Configuration [He]2s22p4
Number of Isotopes 3
Electron Affinity (kJ/mol) 140.9788
First Ionization Energy (kJ/mol) 1313.9
Second Ionization Energy (kJ/mol) 3388.2
Third Ionization Energy (kJ/mol) 5300.3
Electronegativity 3.44
Polarizability (Å3) 0.793
Atomic Weight 15.999
Atomic Volume (cm3/mol) 13.9
Ionic Radius2- (pm) 126
Ionic Radius1- (pm) ---
Atomic Radius (pm) 73
Ionic Radius1+ (pm) ---
Ionic Radius2+ (pm) ---
Ionic Radius3+ (pm) ---
Common Oxidation Numbers -2
Other Oxid. Numbers -1, +1, +2
In Earth's Crust (mg/kg) 4.61×105
In Earth's Ocean (mg/L) 8.57×105
In Human Body (%) 6.3%
Regulatory / Health
CAS Number 7782-44-7
OSHA Permissible Exposure Limit No limits
OSHA PEL Vacated 1989 No limits
NIOSH Recommended Exposure Limit No limits
Mineral Information Institute
Jefferson Accelerator Laboratory


The name derives from the Greek oxys for "acid" and genes for "forming", since the French chemist Antoine-Laurent Lavoisier originally thought that oxygen was an acid-producer because by burning phosphorus and sulfur and dissolving them in water, he was able to produce acids.

For many centuries, workers occasionally realized that air was composed of more than one component. The behavior of oxygen and nitrogen as components of air led to the advancement of the phlogiston theory of combustion, which captured the minds of chemists for a century. Oxygen was prepared by several workers, including Bayen and Borch, but they did not know how to collect it, did not study its properties, and did not recognize it as an elementary substance.

Oxygen was discovered independently by the Swedish pharmacist and chemist Carl-Wilhelm Scheele in 1771 and the English clergman and chemist Joseph Priestly in 1774. Scheele's Chemical Treatise on Air and Fire was delayed in publication until 1777, and Priestly, whose findings were published first, is credited with the discovery.


Ozone (O3), a highly active compound, is formed by the action of an electrical discharge or ultraviolet light on oxygen.

3O2 + hv → 2O3

Ozone's presence in the Earth's atmosphere (amounting to the equivalent of a layer 3 millimeters (mm) thick under ordinary pressures and temperatures) helps prevent harmful ultraviolet rays of the sun from reaching the Earth's surface. Pollutants in the atmosphere may have a detrimental effect on this ozone layer. Ozone is toxic and exposure should not exceed 0.2 mg/m3 (8-hour time-weighted average - 40-hour work week). Undiluted ozone has a bluish color. Liquid ozone is bluish black and solid ozone is violet-black.


Oxygen has three isotopes. Natural oxygen is a mixture of three isotopes. Naturally occurring oxygen-18 (18O) is stable and available commercially, as is water (H2O with 15% 18O). Commercial oxygen consumption in the U. S. is estimated at 20 million short tons per year and the demand is expected to increase substantially.

Oxygen enrichment of steel blast furnaces accounts for the greatest use of the gas. Large quantities are also used in making synthesis gas for ammonia and methanol, ethylene oxide, and for oxy-acetylene welding.

Air separation plants produce about 99% of the gas, while electrolysis plants produce about 1%.


Oxygen is the third most abundant element found in the sun, and it plays a part in the carbon-nitrogen cycle, the process once thought to give the sun and stars their energy. Oxygen under excited conditions is responsible for the bright red and yellow-green colors of the Aurora.

A gaseous element, oxygen forms 21% of the Earth's atmosphere by volume and is obtained by liquefaction and fractional distillation. The atmosphere of Mars contains about 0.15% oxygen. The element and its compounds make up 49.2%, by weight, of the Earth's crust. About two-thirds of the human body and nine-tenths of water is oxygen.

In the laboratory oxygen can be prepared by the electrolysis of water or by heating potassium chlorate with manganese dioxide as a catalyst.


Oxygen is prepared for commercial use by the liquefaction and fractional distillation of air and by the electrolysis of water, although the latter process is more expensive.

2H2O(liq) + electricity → 2H2(g) + O2(g)

In the laboratory it can be prepared by the electrolysis of water or by heating potassium chlorate with manganese dioxide as a catalyst.

2KClO3(s) + heat → 2KCl(s) + 3O2(g)

Oxygen is very reactive and capable of combining with most elements. It is a component of hundreds of thousands of organic compounds. It is essential for respiration of all plants and animals and for practically all combustion reactions.

Oxygen enrichment for basic-oxygen steelmaking furnaces is the greatest industrial use of the gas. Large quantities are also used in making synthesis gas for ammonia and methanol, ethylene oxide, and for oxy-acetylene welding. Oxygen is utilized in medicine in the treatment of respiratory diseases and is used to aid respiration in marines and passengers of high-flying planes and spaceships. Liquid oxygen is used as an oxidizer in the fuel systems of large rockets.



Kubiszewski, I., & Institute, M. (2011). Oxygen. Retrieved from


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