Facts About Oxygen

Atomic Number: 8
Atomic Symbol: O
Atomic Weight: 15.9994
Melting Point: -361.82 F (-218.79 C)
Boiling Point: -297.31 F (-182.95 C)

Word origin: Oxygen is a combination of two Greek words: oxys, meaning acid, and genes, meaning forming.

Discovery: Although Joseph Priestley and Carl Wilhelm Scheele both discovered oxygen about the same time, Priestly generally gets the credit.

Until 1961, the atomic weight of oxygen was used as a standard of comparison for each of the other elements until 1961 when the International Union of Pure and Applied Chemistry adopted carbon-12 as the new base point. [See Periodic Table of the Elements]

Properties of oxygen

Oxygen gas is colorless, odorless and tasteless. The liquid and solid forms are a pale blue color. Because of its highly reactive nature, oxygen is a component of hundreds of thousands of organic compounds and combines with most elements.

Oxygen is the third most abundant element found in the sun, and has a key role the carbon-nitrogen cycle, the process once thought to give the sun and stars their energy.

Oxygen forms 21 percent of Earth's atmosphere by volume. The atmosphere of Mars contains about 0.15 percent oxygen.

Oxygen accounts for two-thirds of the mass of the human body and nine-tenths of the mass of water. Nearly half of the mass of Earth's crust is made up of oxygen.

Under excited conditions, oxygen is responsible for the aurora borealis’ bright red and yellow-green colors.

Oxygen has nine isotopes. Natural oxygen is a mixture of three isotopes. Oxygen-18, which occurs naturally, is stable and available commercially, as is water (H2O with 15 percent 18O).


Ozone, or trioxygen, consists of three oxygen atoms. It is a highly active compound and is formed by the action of an electrical discharge or ultraviolet light on oxygen. Ozone forms a protective layer in the atmosphere (amounting to the equivalent of 3 millimeters thick under ordinary pressures and temperatures) that helps prevent harmful ultraviolet rays of the sun from reaching the earth's surface.

Oxygen mask
Hospitals frequently prescribe oxygen for patients with respiratory ailments.
Credit: ostill | Shutterstock

Pollutants in the atmosphere may have a detrimental effect on this ozone layer. Ozone is toxic and exposure should be limited. Undiluted ozone has a bluish color. Liquid ozone is bluish-black, and solid ozone is violet-black.

Uses of oxygen

All life relies on oxygen for respiration. Hospitals frequently prescribe oxygen for patients with respiratory ailments.

In the United States, commercial oxygen consumption is estimated at 20 million short tons per year, and the demand is expected to rise. 

Oxygen is essential for combustion. Liquid oxygen, combined with liquid hydrogen, makes an excellent rocket fuel.

Oxygen plays a vital role in smelting steel and in oxyacetylene welding. Oxygen enrichment of steel blast furnaces accounts for the most significant use of the gas. It also takes large quantities of oxygen synthesis gas for ammonia and methanol, ethylene oxide, and for oxyacetylene welding.

(Source: Los Alamos National Laboratory)

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