Silicon

Silicon, Si, is a non-metallic main group element, found in Group IVb of the periodic table.

Atomic Number : 14
Atomic Mass : 28.086

Discovery

Silicon in the amorphous form was prepared by Berzelius in 1823AD

Silicon in the crystalline form was prepared by H St Cdeville in 1854AD.

Occurrence

Silicon is the most abundant element on Earth after oxygen.

Silicon exists primarily as silica (in the free state as Quartz, Flint and Sand), and combined with other materials as

Felspar or Orthoclase, K2O.Al2O3.6SiO2,
Kaolinite, Al2O3.2SiO2.2H2O, and
Anorthite, CaO.Al2O3.2SiO2.

Extraction

Preparation

Amorphous Silicon

Amorphous Silicon is prepared in the laboratory by heating potassium in an atmosphere of silicon tetrafluoride.


		SiF4   +   4 K   ==>    Si    +    4 HF

Crystalline Silicon

Crystalline Silicon is prepared in the laboratory by dissolving silicon in aluminium and then cooling the solution, when crystalline silicon separates out of the solution.

Manufacture

Properties

Silicon exists in different allotropic forms which differ in chemical and physical properties.

Amorphous Silicon

is a dark brown powder which on heating in air forms a protective coating of silica which prevents further oxidation,
is insoluble in water and most acids, and
dissolves in hydrofluoric Acid forming fluorosilicic acid.
```
	Si   +   3 HCl   ==>   2 H2   +   H2SiF6	
```

dissolves in sodium hydroxide forming sodium silicate.

	
	Si   +   2 NaOH   + H2O   ==>   2 H2   +   Na2SiO3

Crystalline Silicon

resembles amorphous silicon in many of its chemical reactions but it is less reactive,
consists of dark-gray needles or octahedral plates, which are hard enough to scratch glass.

Reactions

Uses

Silicon is used

in the electronics industry for the manufacture of integrated circuits,
in alloys used in the electrical industry, and
for the manufacture of Silicones, which are important industrial compounds.

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