• 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.

Occurrence of Silicon

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

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

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)

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.

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.

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.