Cesium (Cs)
Cesium (Cs) is a chemical element with atomic number 55, belonging to Group I of the periodic table as the heaviest alkali metal excluding francium. It is a silver-white, highly malleable metal that burns brightly in humid air and can react explosively with water. Natural occurrences of cesium are rare, making up only about 7 parts per million of the Earth's crust, primarily found in minerals such as pollucite and lepidolite, with significant reserves located in countries like Namibia, Zimbabwe, and Canada.
Cesium has various applications, notably in the manufacture of photoelectric cells, vacuum tubes, and in analytical instruments. One of its isotopes, cesium-137, is used in radiation therapy and has been identified by the International Atomic Energy Agency as a material of concern due to its potential use in "dirty bombs." The element was discovered via spectroscopy in 1860 by German scientists Robert Bunsen and Gustav Kirchhoff, who named it after the Latin word for "sky blue." While cesium’s compounds are utilized across several industries, caution is warranted due to the toxicity and radioactivity of some isotopes, particularly cesium-137, which has been linked to serious health incidents in the past.
Cesium (Cs)
Where Found
The element cesium makes up only 7 parts per million of the Earth’s crust. Found only in minerals, it does not occur in its free state naturally. The leading producers are in southwest Africa, the Russian republics, Sweden, and the island of Elba. In North America it is most often found in ores in South Dakota, Maine, and Manitoba, Canada. Significant reserve bases exist in Namibia and Zimbabwe as well as Canada.
Primary Uses
Cesium has significant applications in the manufacture of photoelectric cells and vacuum tubes. One of its isotopes, cesium 137, is used in radiation therapy. Cesium compounds have also served as antishock agents after administration of arsenic drugs. The International Atomic Energy Agency has also identified cesium 137 as one of the radioactive materials that may be used to make “dirty bombs.”
Technical Definition
Cesium (abbreviated Cs), atomic number 55, belongs to Group I of the periodic table of the elements and is the heaviest of the alkali metals (excluding the radioactive francium). It has twenty-two known isotopes, with masses ranging from cesium 123 to cesium 144, with an average atomic weight of 132.905. The only naturally occurring isotope is cesium 133.
Description, Distribution, and Forms
Pure cesium is a silver-white, ductile metal that is extremely malleable. Finely divided cesium produces a blue flame and is easily oxidized by burning brightly in humid air; it may explode in the presence of water. It has a density of 1.9 grams per cubic centimeter, a melting point of 28.5° Celsius, and a boiling point of 705° Celsius.
History
Cesium was discovered and detected by spectroscopy in 1860 by the German scientists Robert Bunsen and Gustav Robert Kirchhoff, who during their analysis detected the two blue lines of cesium and named the element after the word caesius, Latin for “sky blue.” The metal was first isolated by electrolysis in 1881. Cesium compounds are widely distributed in nature in small quantities in various ores. The greatest sources of cesium are the silicatemineral pollucite, which contains up to 34 percent cesium oxide, and camallite. Only 0.002 part per million of cesium exist, in seawater. Detectable quantities are found in plant and animal organisms, mineral waters, and soils. Cesium in conjunction with rubidium and lithium is found in several lepidolite ores in Zimbabwe and South Africa.
Obtaining Cesium
Cesium is obtained by applying the so-called limestone process to lepidolite ore. After treatment of the ore with limestone (known as carbonation), lithium is separated, cesium carbonate is reduced by metallic magnesium, and cesium metal is isolated by condensation of its vapors. Another process for obtaining cesium first produces cesium chloride, which upon heating with a reducing element such as calcium or lithium yields the pure metal. Cesium’s low electronegativity is responsible for its vigorous reaction with oxidizing agents. It reacts readily with most ordinary compounds, such as the halogens, ammonia, nitrogen, carbon monoxide, and even organic compounds such as ethylene and acetylene.
Uses of Cesium
Cesium metal is used in photoelectric cells and in the optical and detecting devices of many analytical instruments. Cesium compounds are used in glass and ceramic production plants, and cesium chloride is used to remove small quantities of oxygen and water during the manufacture of vacuum tubes. Cesium 137 is often used in radiation therapy treatments.
Some of the isotopes of cesium are toxic. Cesium 137 is a radioactive beta-emitter whose ions migrate to the same places in the body that sodium ions go. One of the worst radiation accidents in history occurred in Goiânia, Brazil, in 1987. An abandoned radiotherapy clinic was visited by scavenging inhabitants of the area. They discovered a cesium 137 machine and opened the tube, thus exposing themselves to the harmful rays. Several people died, and about 250 more were contaminated. In February, 2008, the National Research Council mandated the U.S. government to seek alternatives to replace cesium 137.
Bibliography
WebElements.