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1. Hydrocarbons: Alkanes, Alkenes
& Alkynes
10th Class Chemistry | Structures,
Nomenclature, Reactions &
Applications

2. Introduction
• Hydrocarbons: compounds made up of Carbon (C) and Hydrogen (H).
• Main categories:
• • Alkanes → Saturated (single bonds).
• • Alkenes → Unsaturated (double bond).
• • Alkynes → Unsaturated (triple bond).

3. Alkanes (CnH2n+2)
• General Formula: CnH2n+2
• Tetrahedral geometry around carbon atoms.
• Examples: CH4 (Methane), C2H6 (Ethane), C3H8 (Propane).
• Nomenclature: root name + 'ane'.
• Reactions:
• • Complete combustion: CH4 + 2O2 → CO2 + 2H2O
• • Substitution: CH4 + Cl2 → CH3Cl + HCl (UV light)

4. Alkenes (CnH2n)
• General Formula: CnH2n
• Planar structure around double bond carbon atoms.
• Examples: C2H4 (Ethene), C3H6 (Propene).
• Nomenclature: root name + 'ene'.
• Reactions:
• • Combustion: C2H4 + 3O2 → 2CO2 + 2H2O
• • Addition: C2H4 + Br2 → C2H4Br2 (Bromination).
• • Polymerization: n(C2H4) → (C2H4)n (Polyethene).

5. Alkynes (CnH2n-2)
• General Formula: CnH2n-2
• Linear structure around triple bond carbon atoms.
• Examples: C2H2 (Ethyne), C3H4 (Propyne).
• Nomenclature: root name + 'yne'.
• Reactions:
• • Combustion: 2C2H2 + 5O2 → 4CO2 + 2H2O
• • Addition: C2H2 + H2 → C2H4 → C2H6 (Hydrogenation).

6. Formation of Hydrocarbons
• Alkanes: Hydrogenation of alkenes/alkynes.
• Alkenes: Dehydration of alcohols, cracking of alkanes.
• Alkynes: Dehydrohalogenation of dihalides.
• Natural sources: Petroleum, Natural Gas, Coal.

7. Comparison of Hydrocarbons
• Alkanes → Single bond, least reactive, undergo substitution.
• Alkenes → Double bond, reactive, undergo addition reactions.
• Alkynes → Triple bond, highly reactive, undergo addition reactions.

8. Applications
• Alkanes: Fuels (methane, propane, butane).
• Alkenes: Plastics (polyethene, PVC), solvents, alcohol synthesis.
• Alkynes: Welding (oxy-acetylene torch), organic synthesis.

9. Summary
• Hydrocarbons are essential organic compounds.
• Different types depend on C–C bond (single, double, triple).
• Alkanes (CnH2n+2) → Saturated hydrocarbons.
• Alkenes (CnH2n) → Unsaturated, double bond.
• Alkynes (CnH2n-2) → Unsaturated, triple bond.