Silicon is a metalloid and has the second most abundance in earth crust after oxygen, It is not found in elemental form. It forms 95 % of the rocks in the earth. It is found in compounds such as silica, SiO 2, and silicates SiO 2 is found as sand, quartz and mountain crystals in nature. Occurrence of Silicon

Preparation Heating silica with coke at C in electric furnaces. SiO 2 (s) + 2C(s) → Si(s) + 2CO(g) SiCl 4 is heated with H 2 or metals. SiCl 4 (g) + 2H 2 (g) → Si(s) + 4HCl(g) SiCl 4 (g) + 4Na(s) → Si(s) + 4NaCl(s) With strong reducing gents like Cu, Mg and CaCl 2. SiO 2 (s) + 2Mg(s) → Si(l) + 2MgO(s) Heat 800 o C o C

Chemical Properties of Silicon Reactions React with C, O, S and N at high temperatures ( C) Si + O 2 → SiO 2 Si + C → SiC Reacts with halogens. Si(s) + 2F 2 (g) → SiF 4 (g) Si(s) + 2Cl 2 (g) → SiCl 4 (g) React with HF (not other acids) Si + 4HF → SiF 4 + 2H 2 React with hot strong base solutions. Si + 2KOH + H 2 O → K 2 SiO 3 + 2H 2

Silicon Dioxide, SiO 2 It has similar structure to diamond, 57% of Earth crust is SiO2 and silicates. Used to make jeweler, laboratory glassware, various lenses, ultraviolet light-passing glass, fluorescent lamps, light-sensitive electrical measurement instruments and glassware. It does not dissolve in water or acids (except HF). SiO 2 (s) + 4HF(g) → 2H 2 O(l) + SiF 4 (g) SiO 2 is a stable compound. React only strong reducing agents. SiO 2 (s) + 2Mg(s) → Si(s) + 2MgO(s)

Silicates They are composed of SiO 2 and metal oxides Clay: Occurs naturally as alumina silicate, H 4 Al 2 SiO 9. They can be shaped easily when they are wet. Used to prepare pottery, cement, ceramics, rubber and paint. It is a hard substance, when cooled it solidifies, without crystallization and quartz glass is formed.

Glass: The main component of glass are sodium silicate,Na 2 SiO 3, and calcium silicate,CaSiO 3. Glass is hard, brittle, amorphous, transparent, not affected by chemically active substances. Formula of ordinary glass, Na 2 O.CaO.6SiO 2.

Cement: Main component is calcium aluminosilicate. It is used in concrete which is mixture of cement, sand, and stone.

Silicones Polymeric compounds have properties of both hydrocarbons and silicon-oxygen compounds. They are odorless, colorless, inert They are used in hydraulic fluids, enamels, sealing compounds, varnishes, resins and synthetic rubber.

Uses of Silicon In polymers, solar cells, different alloys, cement, glass, clay, jeweler industry…etc.