Interesting Facts About Arsenic

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Arsenic Facts

By Anne Marie Helmenstine, Ph.D.

Arsenic is best known as a poison and a pigment, but it has many other interesting properties. Here are 10 arsenic element facts:

1. Arsenic's symbol is As and its atomic number is 33. It is an example of a metalloid or semimetal, with properties of both metals and nonmetals. It is found in nature as a single stable isotope, arsenic-75. At least 33 radioisotopes have been synthesized. Its most common oxidation states are -3 or +3 in compounds. Arsenic also readily forms bonds with its own atoms.
2. Arsenic occurs naturally in pure crystalline form and also in several minerals, usually with sulfur or metals. In its pure form, the element has three common allotropes: gray, yellow, and black. Yellow arsenic is a waxy solid that converts into gray arsenic after exposure to light at room temperature. Brittle gray arsenic is the most stable form of the element.
3. The element name comes from the ancient Persian word Zarnikh, which means "yellow orpiment." Orpiment is arsenic trisulfide, a mineral that resembles gold. The Greek word "arsenikos" means "potent."
4. Arsenic was known to ancient man and important in alchemy. The pure element was officially isolated in 1250 by the German Catholic Dominican friar Albertus Magnus (1200–1280). Early on, arsenic compounds were used in bronze to increase its hardness, as colorful pigments, and in medicines.
5. When arsenic is heated, it oxidizes and releases an odor similar to that of garlic. Striking various arsenic-containing minerals with a hammer might also release the characteristic odor.
6. At ordinary pressure, arsenic, like carbon dioxide, does not melt but sublimes directly into vapor. Liquid arsenic only forms under high pressure.
7. Arsenic has long been used as a poison, but it's readily detected. Past exposure to arsenic may be assessed by examining hair. Urine or blood tests can assay recent exposure. The pure element and all its compounds are toxic. Arsenic damages multiple organs, including the skin, gastrointestinal tract, immune system, reproductive system, nervous system, and the excretory system. Inorganic arsenic compounds are considered more toxic than organic arsenic. While high doses can cause a quick death, low-dose exposure is also dangerous because arsenic can cause genetic damage and cancer. Arsenic causes epigenetic changes, which are heritable changes that occur without alteration of DNA.
8. Although the element is toxic, arsenic is widely used. It is a semiconductor doping agent. It adds a blue color to pyrotechnic displays. The element is added to improve sphericity of lead shot. Arsenic compounds are still found in certain poisons, such as insecticides. The compounds are often used to treat wood to prevent degradation by termites, fungi, and mold. Arsenic is used to produce linoleum, infrared-transmitting glass, and as a depilatory (chemical hair remover). Arsenic is added to several alloys to improve their properties.
9. Despite the toxicity, arsenic has several therapeutic uses. The element is an essential trace mineral for proper nutrition in chickens, goats, rodents, and possibly humans. It may be added to livestock food to help the animals put on weight. It has been used as a syphilis treatment, cancer treatment, and skin bleaching agent. Some species of bacteria can perform a version of photosynthesis that uses arsenic rather than oxygen to obtain energy.
10. The element abundance of arsenic in the Earth's crust is 1.8 parts per million by weight. Approximately a third of the arsenic found in the atmosphere comes from natural sources, such as volcanoes, but most of the element comes from human activities, such as smelting, mining (especially copper mining), and release from coal-burning power plants. Deepwater wells are commonly contaminated with arsenic.