Periodic Table -> Arsenic
Arsenic DetailsArsenic Symbol:
AsArsenic Atomic Number:
33Arsenic Atomic Weight:
74.922What is Arsenic?
The element Arsenic
is found in the earth's crust, occurring naturally in our planet's environment. It is combined with elements such as sulfur, chlorine, and oxygen and forms different inorganic arsenic compounds. Exposure to levels of arsenic that are higher-than-overage may occur in water, rocks, and soils with naturally occurring high levels. Exposure is also possible in or near hazardous waste sites and workplaces close to such areas. Long-term exposure to low levels of arsenic can result in the appearance of small-size warts and corns and discoloration of the skin. High levels of arsenic are dangerous to human health and can cause death. Exposures to this element are addressed in industry-specific standards for the construction industry, shipyard employment, and the general industry.
Arsenic (atomic number 33, symbol As) occurs as a pure crystal as well as in many minerals. This element is a metalloid and is found in different allotropes (structural modifications of chemical elements). The grey from has found important applications in the industry. Metallic arsenic is mainly used to strengthen alloys of lead (e.g. in automotive batteries) and copper. Arsenic is also among the most commonly used semiconductors and makes the compound gallium arsenide, which is optoelectronic. Arsenic, together with its compounds, is employed in the production of insecticides, herbicides, and pesticides. Some bacteria species are arsenic-tolerant and use the compounds of arsenic as respiratory metabolites. Arsenic has a toxic effect on more complex life forms because of the interaction of protein thiols and arsenic ions.
Between the 18th and 20th century, the compounds of arsenic were used for medicinal purposes. Now, some compounds are used as a wood preservative and in the production of special kind of glass. Gallium arsenide, for example, converts electronic currents into laser light. An important dopant gas is the arsine gas AsH3, which is used in the microchip industry. Due to its very toxic nature, strict guidelines for its use have been developed.
The three allotropic forms of arsenic are grey, black, and yellow. Its stable form is a crystalline, bristle, silver-gray solid. Metallic arsenic is brittle and forms arsenic trioxide through oxidation when heated. While the non-metallic arsenic is less reactive, it dissolves at high temperatures when reacting with alkalis and strong oxidizing acids.
Arsenic is found in three types of compounds – alloys, organoarsenic compounds, and inorganic compounds. The element forms crystalline, odorless, and colorless oxides. Well-know inorganic compounds are triiodide, tribromide, trichloride, and trifluoride.There is a variety of organoarsenic compounds as well. Several of them were developed during the First World War as chemical warfare agents. Among them are lewisite and adamsite, which is a vomiting agent. Cacodylic acid is formed from arsenic trioxide through methylation, a reaction that is unique in phosphorus chemistry.
In the environment, arsenic comes from a variety of sources. Volcanoes, for example, release some 3,000 tons every year while methylarsines, formed by the activity of microorganisms, make for additional 20,000 a year. Arsenic is produced by human activity in much greater quantities, however, especially when fossil fuels are burnt.
This element is very hard to convert into volatile and water-soluble products. Large concentrations of arsenic are unlikely to occur in a certain area because it is a fairly mobile element. However, because arsenic spreads easily, environmental pollution becomes an issue. Moreover, even when the element is immobile, it cannot be mobilized.
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