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Si

SILICON

(L. silex, silicis, flint)

Si at. wt. 28.086
   at. no. 14
   m.p. 1410°C
   b.p. 2355°C 
   sp. gr. 2.33 (25°C)
   valence 4

**Electronic configuration**
SHELL	K	L	M	N	O	P	Q
SUB SHELL	He	Neon	Argon	Krypton	Xenon	Radon	Eka-radon
SUB SHELL	1s	2s 2p	3s 3p	3d 4s 4p	4d 5s 5p	4f 5d 6s 6p	5f 6d 7s 7p
Silicon	1s²2s²2p⁶3s²3p²
Symbol	³S₀

Silicon, Davy in l800 thought silica to be a compound and not an element; later in 1811, Gay Lussac and Thenard probably prepared impure amorphous silicon by heating potassium with silicon tetrafluoride. Benelius, generally credited with the discovery, in 1824 succeeded in preparing amorphous silicon by the same general method 'as used earlier, but he purified the product by removing the fluo4licates by re- peated 'washings. Deville in 1854 firs't' prepated crystalline silicon, the second allotropic form of the element.'Silicon is preserit in the sun and stars and is a principal component of a class" otmeteorites known as aerolites. It is also a corriponent of tektites, a natural glass of uncertain origin, but believed by some to be ejected lunar material from the crater Tycho. Silicon makes up 25.7% of the earth's crust, by weight, afid is the second most abundant element, being exceeded o'nly by oxygen. Silicon is not found free in nature, but occurs chiefly as the oxide, and as silicates. Sand, quartz, rock crystal, amethyst, agate, flint, jasper, and opal are some of the forms in which the oxide appears. Granite, homblende, asbestos, feldspar, 'clay, mica, etc. are but" a' few of the i numerous silicate minerals. Silicon is prepared com- mercially by heating silica and carbon in an electric furnace, using carbon electrodes. Several other methods can be used for preparing the element. Amorphous silicon can be pre- pared as a brown powder, which can be easily melted or vaporized. Crystalline silicon has a metallic luster and grayish color. The Czochralski process is commonly used to produce single crystals of silicon used for solid-st4te or semiconductor devices. Hyper-pure silicon can be prepared by the thermal decomposition of ultra-pure trichlorosilane in a hydrogen atmosphere, and by a vacuum float zorie process. This product can be doped with boron, gallium, phosphorus, or arsenic, etc. to produce silicon for use in transisto?s, solar cells, rectifiers, and other solid-state devices which are used extensively in the electronics and space-age, industries. Silicon is a relatively inert element, but it is a'ttacked b? halogens and dilute alkali. Most acids, except hydrbfluoric, do 'not affeht it. Silicones are important products of silic' on. They may be' 'prepared by hydrolyzing a silicon organic chloride, such as ai'm'e'thj;'l silicon chloride. Hydrolysis and condejisation of various substituted chloro- silanes can be used to produce a very great number of poly- meric products, or silicones, ranging from liquids to 'hard, glass-like solids with many useful properties. Elemental silicon t?ansmits mdre than 95 % of all wavelengths of infra- red, from 1.3 'to 6.7 micrdns. Silicon is one of man's most useful elements. In the' fdrm of sand and clay it is used to make concrete and 'brick; it is a useful refractory material for high-temperature work, and in the form of s'ilicates it is used in making enamels, pottery, etc. Silica, as sand, is a principal ingredient of glass, one of the most inexpensive of materials with excellent mechanical, optical, thermal, and electrical properties. Glass can be made in a very great variety of shapes, and is used as coritainers, window glass, insulators, and thousands of other uses. Sflicon tetra- chloride can be used to iridize,glass. Silicon is important in plant and animal life. Diat6ms' in both fresh and salt witer extract silica from the water to build up their c,ell walls. Silica is present in ashes of,~plants and in the human skeleton. Silicon is an important ingredient in stee~; silicon carbide is one of the most important abrasives and has been used in lasers to produce coherent light of 4560 A. Regular grade silicon (97%) costs about 20 cents/lb. Silicon 99.7% pure costs about $7/lb.; hyper-pure silicon may cost as much as $100/lb. Miners, stonecutters, and others engaged in work where siliceous dust is breathed in large quantities often develop a serious lung disease known as silicosis.

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Si

SILICON

(L. silex, silicis, flint)

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