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Silicon is a metalloid and has the second most abundance in earth crust after oxygen,

Occurrence of Silicon. 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

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Silicon is a metalloid and has the second most abundance in earth crust after oxygen,

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  1. Occurrence of Silicon • 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, SiO2, and silicates • SiO2 is found as sand, quartz and mountain crystals in nature.

  2. Preparation • Heating silica with coke at 3000 0C in electric furnaces. SiO2(s) + 2C(s) → Si(s) + 2CO(g) • SiCl4 is heated with H2 or metals. • SiCl4(g) + 2H2(g) → Si(s) + 4HCl(g) • SiCl4(g) + 4Na(s) → Si(s) + 4NaCl(s) • With strong reducing gents like Cu, Mg and CaCl2. • SiO2(s) + 2Mg(s) → Si(l) + 2MgO(s) Heat 800oC 600-700oC

  3. Chemical Properties of Silicon Reactions • React with C, O, S and N at high temperatures (1200 0C) • Si + O2 → SiO2 Si + C → SiC • Reacts with halogens. • Si(s) + 2F2(g) → SiF4(g) Si(s) + 2Cl2(g) → SiCl4(g) • React with HF (not other acids) • Si + 4HF → SiF4 + 2H2 • React with hot strong base solutions. • Si + 2KOH + H2O → K2SiO3 + 2H2

  4. Silicon Dioxide, SiO2 • 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). • SiO2(s) + 4HF(g) → 2H2O(l) + SiF4(g) • SiO2 is a stable compound. React only strong reducing agents. SiO2(s) + 2Mg(s) → Si(s) + 2MgO(s)

  5. Silicates • They are composed of SiO2 and metal oxides • Clay: • Occurs naturally as alumina silicate, • H4Al2SiO9. 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.

  6. Glass: • The main component of glass are sodium silicate,Na2SiO3, and calcium silicate,CaSiO3. Glass is hard, brittle, amorphous, transparent, not affected by chemically • active substances. Formula of ordinary • glass, Na2O.CaO.6SiO2.

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

  8. 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.

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

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