JSS 3: HYDROCARBON

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Hydrocarbons are organic compounds that contain only carbon and hydrogen atoms.
The general molecular formula of a hydrocarbon is CₓHᵧ, where x and y represent the number of carbon and hydrogen atoms, respectively.

Examples of hydrocarbons include: Methane (CH₄), Ethene (C₂H₄), Ethyne (C₂H₂), Benzene (C₆H₆) etc 

Hydrocarbons are classified into two main groups according to their structure:
1. Aliphatic hydrocarbons e.g. Alkane, alkene, alkyne and cycloalkane
2. Aromatic hydrocarbons e.g. Benzene 

                Sources of hydrocarbons 
The natural sources of hydrocarbons are:
1. Natural gas
2. Crude oil (Petroleum)
3. Coal
They are known as fossil fuels.
•Natural gas is a gaseous fuel
•Petroleum is a dark viscous liquid fuel
•Coal is a solid fuel 

               Properties of Alkanes
1. They are saturated hydrocarbons containing only single covalent bonds (C–C).
2. They have the general formula CₙH₂ₙ₊₂.
3. They are less reactive than other hydrocarbons.
4. They are insoluble in water but soluble in organic solvents.
5. They burn in oxygen to produce carbon dioxide and water, releasing heat.

Examples:
General formula of alkane: CₙH₂ₙ₊₂
When:
n=1, CH₄: Methane
n=2, C₂H₆: Ethane:  CH₃–CH₃
n=3, C₃H₈: Propane: CH₃–CH₂–CH₃
n=4, C₄H₁₀: Butane: CH₃–CH₂–CH₂–CH₃
n=5, C₅H₁₂: Pentane:  CH₃–CH₂–CH₂–CH₂–CH₃

              Properties of Alkenes
1. They are unsaturated hydrocarbons containing at least one carbon-carbon double bond (C=C).
2. They have the general formula CₙH₂ₙ.
3. They are more reactive than alkanes.
4. They undergo addition reactions (e.g., with hydrogen, bromine, and chlorine).
5. They decolourise bromine water, showing the presence of a double bond.
General Formula of Alkene: CₙH₂ₙ
When:
n = 2, C₂H₄: Ethene: CH₂=CH₂
n = 3, C₃H₆: Propene: CH₂=CH–CH₃
n = 4, C₄H₈: Butene: CH₂=CH–CH₂–CH₃
n = 5, C₅H₁₀: Pentene: CH₂=CH–CH₂–CH₂–CH₃
n = 6, C₆H₁₂: Hexene: CH₂=CH–CH₂–CH₂–CH₂–CH₃

            Properties of Alkynes
1. They are unsaturated hydrocarbons containing at least one carbon-carbon triple bond (C≡C)
2. They have the general formula CₙH₂ₙ₋₂.
3. They are highly reactive because of the triple bond.
4. They undergo addition reactions readily.
5. They burn with a luminous, smoky flame due to their high carbon content.
General Formula of Alkyne: CₙH₂ₙ₋₂
When:
n = 2, C₂H₂: Ethyne (Acetylene): CH≡CH
n = 3, C₃H₄: Propyne: CH≡C–CH₃
n = 4, C₄H₆: Butyne: CH≡C–CH₂–CH₃
n = 5, C₅H₈: Pentyne: CH≡C–CH₂–CH₂–CH₃
n = 6, C₆H₁₀: Hexyne: CH≡C–CH₂–CH₂–CH₂–CH₃

          Properties of Cycloalkanes
1. They are saturated hydrocarbons with carbon atoms arranged in a ring.
2. They have the general formula CₙH₂ₙ.
3. They contain only single carbon-carbon bonds.
4. They are insoluble in water but soluble in organic solvents.
5. They undergo substitution reactions similar to alkanes.

General Formula of Cycloalkane: CₙH₂ₙ

When:
n = 3, C₃H₆: Cyclopropane:
      CH₂
     /    \
  CH₂ - CH₂

   Properties of Aromatic Hydrocarbons
1. They contain one or more benzene rings.
2. They are very stable.
3. They undergo substitution reactions rather than addition reactions.
4. They usually burn with a smoky (sooty) flame because of their high carbon content.
5. They are generally insoluble in water but soluble in organic solvents.

Class activities 
1. Hydrocarbons are compounds that contain only ________. (a) Carbon and hydrogen (b) Carbon and oxygen (c) Hydrogen and oxygen (d) Carbon, hydrogen and nitrogen

2. Which of the following is an example of an alkane? (a) CH₄ (b) C₂H₄ (c) C₂H₂ (d) C₆H₆

3. The general formula of alkenes is ________. (a) CₙH₂ₙ₊₂ (b) CₙH₂ₙ (c) CₙH₂ₙ₋₂ (d) CₙHₙ

4. Which hydrocarbon contains a carbon-carbon triple bond? (a) Alkane (b) Alkene (c) Alkyne (d) Cycloalkane

5. Which of the following is a natural source of hydrocarbons? (a) Coal (b) Plastic (c) Glass (d) Rubber

6. Which hydrocarbon decolourises bromine water? (a) Alkane (b) Alkene (c) Cycloalkane (d) Benzene

7. Cycloalkanes are hydrocarbons in which the carbon atoms are arranged in a ________. (a) Straight chain (b) Branched chain (c) Ring (d) Zigzag chain

8. Which of the following is an aromatic hydrocarbon? (a) Methane (b) Ethene (c) Ethyne (d) Benzene

9. Which property is common to alkanes and cycloalkanes? (a) They contain double bonds. (b) They contain triple bonds. (c) They are saturated hydrocarbons. (d) They readily decolourise bromine water.

10. The general formula of alkynes is ________. (a) CₙH₂ₙ₊₂ (b) CₙH₂ₙ (c) CₙH₂ₙ₋₂ (d) CₙHₙ

11. Hydrocarbons are classified into ________ main groups. (a) One (b) Two (c) Three (d) Four

12. Which of the following belongs to the aliphatic hydrocarbons? (a) Benzene (b) Alkane (c) Naphthalene (d) Toluene

13. Petroleum is also known as ________. (a) Natural gas (b) Coal (c) Crude oil (d) Coke

14. Natural gas is a ________ fuel. (a) Solid (b) Liquid (c) Gaseous (d) Semi-solid

15. Coal is a ________ fuel. (a) Gaseous (b) Liquid (c) Solid (d) Vapour

16. Which of the following is the simplest alkene? (a) Ethene (b) Propene (c) Butene (d) Pentene

17. Which of the following is the simplest alkyne? (a) Methyne (b) Ethyne (c) Propyne (d) Butyne

18. Aromatic hydrocarbons contain one or more ________. (a) Double bonds only (b) Triple bonds only (c) Benzene rings (d) Cycloalkane rings

19. Which of the following hydrocarbons has the formula C₃H₈? (a) Ethane (b) Propane (c) Butane (d) Pentane

20. The three natural sources of hydrocarbons are natural gas, petroleum and ________. (a) Water (b) Air (c) Coal (d) Limestone.



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