A Description of Selenium
Atomic Number: 34 Atomic Radius: 117 pm Atomic Symbol: Se Melting Point: 220.5 C Atomic Weight: 78.96 Boiling Point: 685 C Electron Configuration: [Ar]4s23d104p4 Oxidation States: 6, 4, -2
Selenium is a non metallic chemical element, member of the group XVI of the periodic table. In chemical activity and physical properties it resembles sulfur and tellurium. Selenium appears in a number of allotropic forms: the most popular are red amorphous powder, a red crystalline material, and a gray crystalline metallike form called metallic selenium. This last form conducts electricity better in the light than in the dark and is used in photocells. Selenium burns in air and is unaffected by water, but dissolves in concentrated nitric acid and alkalis.
History
(Gr. Selene: moon) Discovered by Berzelius in 1817, who found it associated with tellurium (named for the earth).
Production
Selenium is found in a few rare minerals such as crooksite and clausthalite. In years past it has been obtained from flue dusts remaining from processing copper sulfide ores, but the anode metal from electrolytic copper refineries now provide the source of most of the world's selenium. Selenium is recovered by roasting the mud with soda or sulfuric acid, or by smelting them with soda and niter.
Properties
Selenium exists in several allotropic forms, although three are generally recognized.
Selenium can be prepared with either an amorphous or a crystalline structure.
The color of amorphous selenium is either red (in powder form) or black (in vitreous form). Crystalline monoclinic selenium is a deep red; crystalline hexagonal selenium, the most stable variety, is a metallic gray.
Selenium exhibits both photovoltaic action, where light is converted directly into electricity, and photoconductive action, where the electrical resistance decreases with increased illumination. These properties make selenium useful in the production of photocells and exposure meters for
Selenium is a non metallic chemical element, member of the group XVI of the periodic table. In chemical activity and physical properties it resembles sulfur and tellurium. Selenium appears in a number of allotropic forms: the most popular are red amorphous powder, a red crystalline material, and a gray crystalline metallike form called metallic selenium. This last form conducts electricity better in the light than in the dark and is used in photocells. Selenium burns in air and is unaffected by water, but dissolves in concentrated nitric acid and alkalis.
History
(Gr. Selene: moon) Discovered by Berzelius in 1817, who found it associated with tellurium (named for the earth).
Production
Selenium is found in a few rare minerals such as crooksite and clausthalite. In years past it has been obtained from flue dusts remaining from processing copper sulfide ores, but the anode metal from electrolytic copper refineries now provide the source of most of the world's selenium. Selenium is recovered by roasting the mud with soda or sulfuric acid, or by smelting them with soda and niter.
Properties
Selenium exists in several allotropic forms, although three are generally recognized.
Selenium can be prepared with either an amorphous or a crystalline structure.
The color of amorphous selenium is either red (in powder form) or black (in vitreous form). Crystalline monoclinic selenium is a deep red; crystalline hexagonal selenium, the most stable variety, is a metallic gray.
Selenium exhibits both photovoltaic action, where light is converted directly into electricity, and photoconductive action, where the electrical resistance decreases with increased illumination. These properties make selenium useful in the production of photocells and exposure meters for