Nomenclature
CAS number: 7440-21-3
Description and references
Si; at. wt 28.0855; at. no. 14; valence 4,
also 2. Group IVA (14). 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 decompn 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, US 3041144 (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. Colvin, Chem. Soc. Rev. 7, 15 (1978);
I. Fleming, ibid. 10, 83 (1981); L. A. Paquette, Science 217, 793 (1982).
Properties
Black to gray, lustrous, needle-like crystals
or octahedral platelets (cubic system). The amorphous form is a dark
brown powder. Poor conductor of electricity. d425 2.33. mp 1410°. Average heat
capacity (16-100°): 0.1774 cal/g/°C. Lattice constant (25°): 5.41987 ×
10-8 cm. Compressibility (V/V0) at 25 × 103 kg/cm2: 0.978; at 100 × 103 kg/cm2: 0.940, Gmelins, Silicon (8th ed.) 15B (1959) p 57. Dielectric const: 13. Covalent
bond ionization energy at 0 K = 1.2 ev. Band gap: 1.106 ev. Impurity
atom ionization energy: ≈0.04 ev. Intrinsic resistivity at 300 K
= 0.23 megohm. Electron mobility at 300 K: 1500 cm2/volt/sec.
Hole mobility at 300 K: 500 cm2/volt/sec. Intrinsic
charge density at 300 K: 1.5 × 1010. Electron diffusion
constant at 300 K: 38. Hole diffusion constant at 300 K: 13. Practically
insol in water. Attacked by hydrofluoric or a mixture of hydrofluoric
and nitric acids (depending upon cryst modifications). Soluble in
molten alkali oxides. Burns in fluorine, chlorine.Caution
Potential symptoms of overexposure
are irritation of eyes, skin, upper respiratory system; cough. See NIOSH Pocket Guide to Chemical
Hazards (DHHS/NIOSH 97-140, 1997) p 278.Use
In making silanes and silicones, 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.