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SeSe at. wt. 78.96 at. no. 34 m.p. 217°C (gray) b.p. 684.9&plusm;1.0°C (gray) sp. gr. 4.79 (gray) sp. gr. 4.28 (vitreous) valence - 2, +4, or +6.
| SHELL | K | L | M | N | O | P | Q |
| SUB SHELL | He | Neon | Argon | Krypton | Xenon | Radon | Eka-radon |
| 1s | 2s 2p | 3s 3p | 3d 4s 4p | 4d 5s 5p | 4f 5d 6s 6p | 5f 6d 7s 7p | |
| Selenium | 1s22s22p63s23p63d104s24p4 | ||||||
| Symbol | 3P2 | ||||||
Selenium was discovered by Berzelius'in 1817, who found it associated with tellurium, named for the earth. Selenium is found in a few rare minerals, s'uch as crooksite and clausthalite. In years !%ast it has been obtained from flue dusts remaining from' processing copper sulfide ores, but the anode muds from electrolytic copper refineries now provide tht source of most of the world's selenium. Selenium is recovered by roasting the muds with soda or sulfuric acid, or by smelting them with soda and niter. Selenium exists in several allo- tropic forms. Three are generally recognized, but as many as six have been claimed. Selenium can be prepared with either' an amorphous or crystalline structure. The color of amorphous selenium is either red, in powder fonrr, or black, in vitreous form. Crystalline monoclinic selenium is 'a deep red; crystalline hexagonal selenium, the most stable variety, is a metallic gray. Natural selenium contains six stable iso- topes. Fourteen other nuclides and isomers have been characterized. The element is a member of the sulfur family and resembles sulfur both in its various forms and in its compounds. Selenium exhibits both photovoltaic action,. where light is converted directly into electric' Ity, and p'hot~ conductive action, where the electrical resistance decreases with increased,iltumination. These properties make selenium useful in the production of photo~ells and exposure meters for photographic use, as well as solar cells. Selenium is also able to convert a.c. electricity to' d.c., and is extensively used in rectifiers. Below its melting point selenium is a p~type semiconductor, and is finding many uses in electronic and solid state applications. It is used in Xerography for re- producing and copying documents, letters, etc. It is used by the glass industry to decolorize glass and to make ruby- colored glasses and enamels. It is also used as a photographic toner, and as an additive to" stainless steel. Elemental selenium has been said to be practically nontoxic; however, hydrogen selenide and other~ selenium compounds are extremely toxic, and resemble arsenic in its physiological reactions. Hydrogen selenide in a concentration of 1.5 ppm. is intolerable 'to man. Selenium occurs in some soils in amounts sufficient to produce serious effects on animals feeding on plants, such as locoweed, grown in such soils. The maximum allowable concentration of selenium com- pounds in air has been recommended to be 0.1 mg/cu meter. Selenium is priced at about $5/lb. It is also available in hig'h- purity form at a somewhat higher cost.
© 1999 F. Davies
Delphi O.E.M. Co.
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