Oxygen (O)
Oxygen (O) is a vital element with the atomic number 8, making up approximately 46.6 percent of the Earth's crust by weight, 85.8 percent of the Earth's waters, and about 23 percent of the atmosphere. It exists primarily in the form of oxides and silicates and plays a crucial role in various biological and chemical processes. In its gaseous state, oxygen is colorless and odorless, and it can form compounds with nearly all elements, except those of the helium family. Elemental oxygen occurs in different forms, including the diatomic molecule (O2) and ozone (O3), contributing to essential life processes like respiration in both terrestrial and marine environments.
Historically, the discovery of oxygen is attributed to Carl Scheele and Joseph Priestley in the 18th century, with Antoine-Laurent Lavoisier later identifying it as an element and explaining its role in combustion. Oxygen has numerous applications, particularly in the steel and chemical industries, where it is used for welding and the production of various chemicals. Additionally, it is crucial in healthcare for treating respiratory conditions and is utilized in hyperbaric chambers for specific medical treatments. With its diverse roles in nature and industry, oxygen is indispensable for life and technological advancement.
Oxygen (O)
Where Found
Oxygen is the most abundant in the Earth’s crust (46.6 percent by weight), occurring mainly as oxides and silicates of metals. The earth’s waters are 85.8 percent oxygen by weight, and the atmosphere is 23.0 percent oxygen. The combined weight of oxygen in the crust, hydrosphere, and is about 50 percent.
Primary Uses
In addition to its importance in the combustion of food for energy by living organisms, oxygen has many commercial applications. It is used in the iron and steel industry, in rocket propulsion, in chemical synthesis, and to hasten the aerobic digestion of sewage solids.
Technical Definition
Oxygen (abbreviated O), atomic number 8, belongs to Group VI of the periodic table of the elements. Its chemical properties are somewhat similar to those of sulfur. It has an average molecular weight of 15.9994 and six naturally occurring isotopes, three of which are radioactive with half-lives on the order of seconds and minutes. At ordinary temperatures, oxygen is a colorless, odorless gas. Its liquid form is pale blue. Oxygen melts at -218° Celsius and boils at -183° Celsius. Oxygen can form compounds with all other elements except the low-atomic-weight elements of the helium family.
Description, Distribution, and Forms
The total content of oxygen in the Earth’s air, crust, and oceans is approximately 50 percent by weight. In chemically combined form, it is found in water and in the clays and minerals of the lithosphere. Despite the fact that it is an active element, forming oxides easily by the process of combustion, elemental oxygen makes up about 23 percent of the atmosphere. Dissolved gaseous oxygen is found in the waters of the Earth, where it provides for the respiration of most marine animals and for the gradual of waste materials in lakes and rivers.
Elemental oxygen is found in three allotropic forms: the ordinary diatomic molecule found in the atmosphere (O2), (O3), and the unstable, nonmagnetic, and rare pale blue O4 form, which decomposes easily to O2. Unstable atomic oxygen is a short-lived species that results from the absorption of ultraviolet radiation by ozone in the upper atmosphere or from electrical discharges.
The solvent properties of water are attributable to the great difference in the strength of attraction for the bonding electrons between hydrogen and oxygen, which makes the resulting molecule very polar. The H2O molecules are attracted to both cations and anions, surrounding them by the attraction of the negative oxygen or the positive hydrogen, respectively. Water also dissociates slightly into H+ and OH- ions. These processes allow water to form hydrates with, and to react with, many compounds.
History
Most chemists agree that the discovery of oxygen was made independently by Carl Scheele in Sweden and Joseph Priestley in England at about the same time. In 1774, Priestley heated mercuric and collected the liberated gas over water. He showed that the “dephlogisticated air” (oxygen) was capable of supporting burning and was respirable. Scheele prepared oxygen in 1771-1772 by heating various carbonates and oxides. Although his experiments were performed earlier than those of Priestley, the latter published his results first. The great French chemist Antoine-LaurentLavoisier was the first to recognize that oxygen is an element, and he was able to explain the combustion process correctly. This explanation revolutionized the field of chemistry and provided the stimulus for the discovery of many new elements.
Obtaining Oxygen
For many years the only means of obtaining oxygen was by the fractional distillation of liquid air. A variation of this basic process is still used when high-purity oxygen is needed. In 1971, an ambient temperature process was introduced by the Linde Division of Union Carbide Corporation. The process uses a pressure cycle in which “molecular sieves” are used to selectively absorb nitrogen from the air. The resulting product contains about 95 percent oxygen and about 5 percent argon and is economically preferable in situations where the argon will not interfere.
Uses of Oxygen
The greatest consumers of oxygen are the steel, chemical, and missile industries. The oldest use of oxygen is in the welding of steel by means of a hot acetylene-oxygen torch. Thicknesses of steel of up to 0.6 meter can be cut by a high-pressure oxygen stream after heating with an acetylene torch. An oxygen stream passed through molten iron can remove carbon impurities by means of combustion to carbon dioxide.
In the chemical industry, oxygen is used for the production of hydrogen from or “synthesis gas”:
CH4 + 0.5 O2 → CO + H2
Other important industrial processes are the manufacture of hydrogen peroxide, sodium peroxide, ethylene oxide, and acetylene.
Large rockets are propelled from their launch pads by the combustion of a fuel similar to kerosene. The fuel and oxygen are kept in liquid form in separate tanks until ignition. (In some rockets the second stage is propelled by the combustion of hydrogen.)
Oxygen has limited but important uses in the health-care industry in the treatment of pneumonia, emphysema, and some heart problems. Hyperbaric chambers provide high-pressure, oxygen-rich atmospheres for the treatment of both carbon monoxide poisoning and decompression sickness (“the bends”).
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