Silicon. Si; at. wt 28.0855; at. no. 14; valence 4, also 2. Three naturally occurring isotopes: 28 (92.18%); 29 (4.71%); 30 (3.12%); artificial isotopes: 25-27; 31; 32. Does not occur free in nature; found as silica (quartz, sand, sandstone) or as silicate (feldspar or orthoclase, kaolinite, anorthite, etc.). Constitutes about 27.6% of the earth's crust; second most abundant element on earth, oxygen being first. Prepd industrially by carbon reduction of silica in an electric arc furnace. Purification by zone refining (see ref. under Germanium). Very pure silicon is obtained by decomp of silicon tetraiodide: Litton, Anderson. J. Electrochem. Soc. 101, 287 (1954); Chem. & Eng. News 34, 5007 (1956). From silicon tetrachloride: Lyon et al., Trans. Electrochem. Soc. 96, 359 (1949); Klyuchnikov, J. Appl. Chem. USSR 29, 139 (1956). By thermal decompn of a chlorosilane: Schering, U.S. pat. 3,041,144 (1962 to Siemens-Schuckertwerke). Review of silicon and its compounds: Rochow, "Silicon" in Comprehensive Inorganic Chemistry vol. 1, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973)
pp 1323-1467; W. Runyan in Kirk-Othmer Encyclopedia of Chemical Technology vol. 20 (Wiley-Interscience, New York, 3rd ed., 1982) pp 826-845. The uses of silicon compounds in organic chemistry: E. W. Calvin, Chem. Soc. Rev. 7, 15 (1978); I. Fleming, ibid. 10, 83 (1981); L. A. Paquette, Science 217, 793 (1982).

Black to gray, lustrous, needle-like crystals or octahedral platelets (cubic system). The amorphous form is a dark brown powder. Poor conductor of electricity. d254 2.33. mp 1410 Average heat capacity (16-100): 0.1774 cal/g/C. Lattice constant (25): 5.41987 x 10-8 cm. Compressibility (V/V0) at 25 x 103 kg/cm2; 0.978; at 100 x 100 kg/cm2: 0.940, Gmelin's Silicon (8th ed.) 15B (1959) p 57. Dielectric const: 13. Covalent bond ionization energy at OK = 1.2 ev. Band gap: 1.106 ev. Impurity atom ionization energy: 0.04 ev. Intrinsic resistivity at 300K = 0.23 megohm. Electron mobility at 300K: 1500 cm2/volt/sec. Hole mobility at 300K: 500 cm2/volt/sec. Intrinsic charge density at 300K: 1.5 x 1010. Electron diffusion constant at 300K: 38. Hole diffusion constant at 300K: 13. Practically insol in water. Attacked by hydrafluoric or a mixture of hydrafluoric and nitric acids (depending upon cryst modifications). Soluble in molten alkali oxides. Burns in fluorine, chlorine.

USE: In making silanes and silicanes, the Si-C bond being about as strong as a C-C bond. In the manuf of transistors, silicon diodes and similar semiconductors. For making alloys such as ferrosilicon, silicon bronze, silicon copper. As a reducing agent like aluminum in high temp reactions.
Ref.: 8438, 1346 pp.
The Merck Index - Eleventh Edition.
Copyright 1989 by Merck & Co., Inc.