ALTONJ. BANKS
what's the use? Silicon
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Symbol: Si .Atomic number: 14 *Atomic weight: 28.0806 .Melting point: 1683.200K aBoilingpoint: 3553.000K Wnsity:2.3360 dm3
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The im~ortanceof this element and its compounds to today's society cannot be overstated. Silicon (L& silicis, flint) is the second most abundant element in the earth's crust. In the earth's crust, silicon is present as silicates or oxides, and these entities occur in chains, rings, and sheets, as well as three-dimensional networks. The oxides of silicon include sand, quartz, flint, as well as the ornamental forms of agate and opai. Silicate forms of the element include asbestos, clay, feldspar, ganite, and mica. These compounds with oxygen proved intractable until the early part of the 19th century. There is some uncertainty about the first isolation of the Dure element. In 1811.. Gav . Lussac and Thenard reportedly prepared impure amor~ h o u silicon s bv heatine silicon tetrafluoride with metallic potassium. In i824, d..;: Brrzclius prepared the free amorphous element by reducing K2BF, with molten potassium.
North Carolina State University Raleigh. NC 27695
A commercial method for production of the free element involves heatine auartzite or sand with carbon in an electric arc furnace. The name silicon was proposed by T. Thomson in 1831 with the "-on" ending pointing out the similarity to both boron and carbon. The amorphous material is brown while the crvstalline element has a blue-aav metallic luster. The u ~ t r a ~ ~element u r e is doped with & s e Nc, boron, gallium, or phosphorus to produce the transistors and other solid-state devices upon which present-day society depends. The element is not particularly reactive, but its compounds are very useful. As a major component of glass, concrete, and brick, its value as a building material is incalculable. The polymeric forms, known as silicones, assume roles from lubricants to medical prostheses. Finally, a serendipitous incident regarding silicon is noteworthy. The abrasive silicon carbide, Sic, was prepared accidentally in 1891 by E. G. Acheson. This substance is intermediate on the Moh's hardness scale between corundum, which has a hardness of 9, and diamond, which has a hardness of 10. Some of these applications are shown on "The Periodic Table Videodisc* in frames 3646536476.
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General References "KC? Dismverer: Exploring the Pmprties of the Chemical Elements";JCE: Soffwam
?I)RII I-, R ( 1. ). . . . . ,. , Handbmk of Chembfry & Physics, 71st ed.; Lide, David. R.. Ed.; Chemical Rubber;
Cleveland, OH, 1990-1991: pp 430. Greenwaad, N. N.;Emshaw,A. C~misf'yofthaEkmnfs;Pergamon, New York,1984; DO .. 37-82. Banks, A. J. LThePetiodieTableYldeodises; JCE: S o A w m 1989. Special Iasue 1.
Volume 69 Number 2 February 1992
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