Carbon

Symbol: C
Atomic number: 6
Valency: 4
Atomic mass: 12 amu.
Electronic configuration: 1s² 2s² 2p²
Electronegativity: 2.5

Position in periodic table:

Carbon is located in group 14 or IVA and 2nd period in the modern periodic table. It is a p-block element. Elements of group 14 are carbon (C), silicon (Si), germanium (Ge), tin (Sn) and lead (Pb).

Allotropes of carbon:

The element carbon exists in the different physical forms known as allotropes of carbon. It has the following allotropes.

1. Crystalline (diamond, graphite and buckminster fullerene)
2. Amorphous (coal, coke, lamp-black, gas-carbon, charcoal)

i. Diamond:

Diamond is the purest form of carbon and it is the hardest compound known.

Structure of diamond:

In a diamond, each carbon atom is tetrahedrally linked with four surrounding carbon atoms. The bond angle is 109.5° and the C-C bond length is 1.54 °A. Carbon atoms are linked with four other carbon atoms through a strong covalent bond which makes the diamond extremely hard with a high melting point.

Properties:

• It is the hardest substance known with a high melting point(3750°C).
• It is transparent to X-rays.
• It has a high density and a high refractive index.
• It is very unreactive.
• It is a bad conductor of electricity.

Uses:

• As jewelry
• Polishing hard materials
• Cutting glass.

ii. Graphite:

It is known as black lead. It is the most stable allotrope of carbon.

Structure of graphite:

In graphite, each carbon atom is linked with three other carbon atoms directly in the same plane to give hexagonal rings. These rings are arranged to form co-planar sheets or layers. These layers are held together by Vander Waal’s force of attraction. The bond angle is 120° and the C-C bond length is 1.41 °A.

Properties

• It is greyish-black solid.
• It is soft and slippery in nature.
• It is a good conductor of electricity.
• It has metallic lusture.
• Its melting point is 3500 °C.

Uses:

• Lubricant for machines and to make crucible.
• To make graphite electrode and lead pencil.
• As moderator.

iii. Buckminster fullerene:

It is the latest discovered allotrope of carbon. It generally consists of a closed cage-like structure as soccer ball. It consists of 60 carbon atoms as 20 hexagons and 12 pentagons.

Properties

• Soluble in organic solvents.
• Easily react with alkali metals.

Uses

• Prepare super-conductor.
• Nanotechnology.

iv. Coal

It is a black or brown solid formed naturally by partial decomposition of vegetable matter in presence of moisture at high temperature and pressure. It is used as fuel as well as a reducing agent.

v. Coke

It is a grayish-black solid obtained by the destructive distillation of coal. It is used as fuel as well as a reducing agent.

vi. Lamp-black:

It is a soft black powder obtained by burning petroleum in the limited supply of air. It is used in the manufacture of black paint, motor tyre, printer, etc.

vii. Gas-carbon:

It is a dense form of deposited carbon during the manufacture of coal gas. It is a good conductor of electricity.

viii. Charcoal:

• Wood charcoal: It is obtained by destructive distillation of wood. It is used in fuel and to prepare gun powder.

• Animal charcoal: It is obtained by destructive distillation of animal bone. It is used as absorbant and disinfectant.

• Sugar charcoal: It is obtained by the action of concentrated sulphuric acid on sugar.
  C₁₂H₂₂O₁₁ + H₂SO₄ → 12C + H₂SO₄.11H₂O
  
  It is used as fuel and for decolorizing the sugar.
  It is used as gun powder materials.

Carbon Monoxide (CO):

Physical Properties:

• It is a colourless gas with a faint smell.
• It is lighter than air.
• It is slightly soluble in water.
• It is a highly poisonous gas.

Chemical Properties

1. Reducing nature:

i. It reduces metallic oxide into free metal.

ZnO + CO → Zn + CO₂
PbO + CO → Pb + CO₂

ii. It reduces Tollens reagent (ammoniacal silver nitrate) into metallic silver.
2[Ag(NH₃)₂]OH (Tollens reagent) + CO → 2Ag (Silver mirror) + 4H₂O + CO₂ + NH₃

iii. It reduces Fehling’s solution (alkaline solution of CuSO₄) into red ppt. of cuprous oxide.
2Cu(OH)₂(Fehling’s solution) + CO → Cu₂O(Red ppt.) + 2H₂O + CO₂

iv. It reduces steam at high temperatures.
CO + H₂O → CO₂ + H₂

v. It reduces I₂O₅ into I₂.
I₂O₅ + 5CO → I₂ + 5CO₂

2. Reactions with metals:

4CO + Ni → Ni(CO)₄ (Nickel tetracarbonyl)
5CO + Fe → Fe(CO)₅ (Iron pentacarbonyl)
8CO + 2Co → Co₂(CO)₈ (Dicobalt octacarbonyl)

3. Action with non-metals:

Uses of CO

• As fuel in water gas (CO+H₂) and producer gas (CO+N₂).
• In the extraction of metals.
• To prepare metal carbonyl.
• As a reducing agent.

Some Important Questions

1. Write the name of crystalline allotropes of carbon. Which is more stable?
2. Write the uses of graphite and diamond.
3. What are water gas and producer gas?
4. Write the action of CO with Cl₂, Ni, NaOH and H₂.
5. Why CO is poisonous gas?