Selenium (Se), a chemical element in the oxygen group (Group 16 [VIa] of the periodic table), closely allied in chemical and physical properties with the elements sulfur and tellurium. Selenium is rare, composing approximately 90 parts per billion of the crust of Earth. It is occasionally found uncombined, accompanying native sulfur, but is more often found in combination with heavy metals (copper, mercury, lead, or silver) in a few minerals. Selenium is a metalloid (an element intermediate in properties between the metals and the nonmetals). The gray, metallic form of the element is the most stable under ordinary conditions; this form has the unusual property of greatly increasing in electrical conductivity when exposed to light. Continue reading from Encyclopedia Britannica
Selenium was discovered by Jöns Jacob Berzelius at Stockholm in 1817. He had shares in a sulfuric acid works and he was intrigued by a red-brown sediment which collected at the bottom of the chambers in which the acid was made. At first he thought it was the element tellurium because it gave off a strong smell of radishes when heated, but he eventually realised that it was in fact a new element. He also noted that it was like sulfur and indeed had properties intermediate between sulfur and tellurium. Berzelius found that selenium was present in samples of tellurium and gave that element its characteristic smell. He also became affected by it personally – it can be absorbed through the skin – and it caused him to experience the bad breath associated with those who work with this element. Continue reading from Royal Society of Chemistry
Selenium is a nutritionally essential element. People need selenium for healthy joints, heart and eyes. It plays a critical role in DNA synthesis, the immune system and the reproductive system. It also helps fight cancer and other diseases. At room temperature selenium is a solid, but not a metal. Other than internal human uses, selenium is also used in manufacturing. It is used to color and decolorize glass. When used in glass and enamels it can create a deep red. It is also used to make photographic toner, photo cells, electric eyes and light meters for cameras. Continue reading from LiveScience
