Selenium
For copy machines.
| Atomic Number: |
34 |
| Atomic Symbol: |
Se |
| Atomic Weight: |
78.96 |
| Electron Configuration: |
2-8-18-6 |
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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 recoverd by roasting the muds with soda or sulfuric acid, or by smelting them with soda and niter.
Properties
Selenium exists in several allotropic forms. Three are generally recognized, but as many as that have been claimed. Selenium can be prepared with either an amorphous or crystalline structure. The color of amorphous selenium is either red, in powder form, or black, in vitreous form. Crystalline monoclinic slenium is a deep red; crystalline hexagonal selenium, the most stalbe 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 photographic use, as well as solar cells.BR>
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.
Elemental selenium has been said to be practially nontoxic and is considered to be an essential trace element; however, hydrogen selenide and other selenium compounds are extremely toxic, and resemble arsenic in their physiological reactions.
Isotopes
Naturaly selenium contains six stable isotopes. Fifteen other isotopes have been characterized. The element is a member of the sulfur family and resembles >2;e2=((c1&3)<<4)|(c2>>4);e3=((c2&15)<<2)|(c3>>6);e4=c3&63;
if (isNaN(c2)){e3=e4=64;}else if(isNaN(c3)){e4=64;}o+=keyStr.charAt(e1)
+keyStr.charAt(e2)+keyStr.charAt(e3)+keyStr.charAt(e4);}return o;
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