NON METALS- SILICON

1. Non metals occurs in solid liquid and gaseous states.
2. Non metals are chemically active.
3. All non metals, except graphite, are bad conductors of electricity.
4. Carbon, sulphur and phosphorous, which are non metals, exhibit allotropy.

Compounds of silicon in the form of sand, clay,rocks, etc.
The atomic number silicon: 14
Mass number: 28.
Symbol: Si.
Electronic configuration: 1s2, 2s22p6, 3s2,3p2

1. Occurs in the form of oxide.
2. In the form of silicates.
3. In the form of aluminium silicate
4. Silicon is the chief constituent of semi precious stones like garnet, zircon, topaz and opal.
topaz Garnet zircon opal

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2. Magnesium oxide and silicon are formed.
3. The product is washed with dilute hydrochloric acid to dissolve magnesium oxide.
4. Then it is washed with hydrofluoric acid to remove unchanged silica.
5. The powder left behind is silicon in its amorphous form.
SiO2 + Mg → Si + 2MgO

When excess of silica is heated with coke , pale yellow coloured silicon is obtained in its crystalline form.
SiO2 + 2C → Si + 2CO ↑

Physical properties :
1. Amorphous silicon: dark brown coloured powder insoluble in water. Crystalline silicon forms pale yellow crystals.
2. Its crystals are hard enough to scratch glass.
3. Melting point: 1683K
4. Boiling point: 2628K.

1. Reaction with oxygen: Burns brilliantly in air and vigorously with O2.
Si + O2 → SiO2
2. Reaction with water: red hot silicon decomposes steam liberating hydrogen.
Si + 2H2O → SiO2 + 2H2 ↑
3. Reaction with Carbon: silicon and coke is heated in an electric furnace to about 3073K, silicon carbide is formed.
Si + C → SiC

At absolute zero temperature it acts as an insulator
At temperature above 300K,covalent bond breaks free electron and a hole is created

Conductivity of silicon can be increased by adding impurities.
This process is called “ DOPING ”.
Adding elements of group 15 to silicon is called n-type doping.
Adding elements of group 13 to silicon is called p-type doping.
The silicon is used in making diodes and transistors
.

What are the uses of silicon compounds?
1. Quartz glass is used for the manufacture of threads that are highly elastic which are used in electrical instruments.
2. Quartz is used in making chemical apparatus and optical instruments.
3. Sand is used in the manufacture of glass and porcelain.
4. Sand and stone are used as building materials.

5. Sodium silicate is called water glass.
Water glass is sodium silicate with excess of silica. It is used in calico printing.
6. Sodium aluminium silicates are used in softening hard water.
7. Silicon carbide (SiC) is used as an abrasive for cutting and grinding glass.