Question

Draw diagrams showing the formation of a double bond and a triple bond between carbon atoms in \(C_2H_4\) and \(C_2H_2\) molecules.

Answer 1

(i) Formation of double bond in C₂H₄ (Ethene)

In ethene, each carbon atom undergoes sp² hybridisation. Each carbon atom forms three sp² hybrid orbitals.

• One sp² orbital of each carbon overlaps with an sp² orbital of the other carbon to form a σ bond. 
• The unhybridised p-orbitals of the two carbon atoms overlap sideways to form a π bond.

Thus, the C=C double bond consists of one σ bond and one π bond.

Diagram showing formation of double bond:

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(ii) Formation of triple bond in C₂H₂ (Ethyne)

In ethyne, each carbon atom undergoes sp hybridisation. Each carbon atom forms two sp hybrid orbitals.

• One sp orbital of each carbon overlaps axially to form a σ bond. 
• The two unhybridised p-orbitals on each carbon overlap sideways to form two π bonds.

Thus, the C≡C triple bond consists of one σ bond and two π bonds.

Diagram showing formation of triple bond:

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Conclusion:

A double bond consists of one σ and one π bond, while a triple bond consists of one σ and two π bonds between the carbon atoms.