Selenium Physical Characteristics

selenium

Selenium  is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium. It rarely occurs in its elemental state in nature, but instead is obtained as a side-product in the refining of other elements.Selenium is found in sulfide ores such as pyrite, where it partially replaces the sulfur.Selenium is a trace mineral that is essential to good health but required only in small amounts. Selenium is incorporated into proteins to make selenoproteins, which are important antioxidant enzymes. The antioxidant properties of selenoproteins help prevent cellular damage from free radicals.
The most stable allotrope of selenium is a dense purplish-gray solid. In terms of structure, it adopts a helical polymeric chain.The Se-Se distance is 2.37 ? and the Se-Se-Se angle is 103°. It is a semiconductor with the unusual property of conducting electricity better in the light than in the dark, and is used in photocells. Gray selenium resists oxidation by air and is not attacked by non-oxidizing acids. With strong reducing agents, it forms polyselenides. Read more:High purity selenium