Silicon: the essentials
Silicon is present in the sun and stars and is a principal component of a class of meteorites known as aerolites. Silicon makes up 25.7% of the earth's crust by weight, and is the second most abundant element, exceeded only by oxygen. It is found largely as silicon oxides such as sand (silica), quartz, rock crystal, amethyst, agate, flint, jasper and opal. Silicon is found also in minerals such as asbestos, feldspar, clay and mica.
Silicon is important in plant and animal life. Diatoms in both fresh and salt water extract silica from the water to use as a component of their cell walls. Silicon is an important ingredient in steel. Silicon carbide is one of the most important abrasives. Workers in environments where silicaceous dust is breathed may develop a serious lung disease known as silicosis.
Silicon: historical information
JΔns Jacob Berzelius is generally credited with the discovery of silicon in 1824. Deville prepared crystalline silicon in 1854, a second allotropic form of the element.
Silicon: physical properties
Silicon: orbital properties
Isolation: there is normally no need to make silicon in the laboratory as it is readily available commercially. Silicon is readily available through the treatment of silica, SiO2, with pure graphite (as coke) in an electric furnace.
SiO2 + 2C → Si + 2CO
Under these conditions, silicon carbide, SiC, can form. However, provided the amount of SiO2 is kept high, silicon carbide may be eliminated.
2SiC + SiO2 → 3Si + 2CO
Very pure silicon can be made by the reaction of SiCl4 with hydrogen, followed by zone refining of the resultant silicon.
SiCl4 + 2H2 → Si + 4HCl