51. Hydrocarbons: Alkanes & Homologous Series

Hydrocarbons: Alkanes & Homologous Series

Based on the video, here are the notes on the simplest group of organic compounds: the alkanes.

1. Key Definitions

  • Organic Chemistry: The study of compounds that contain carbon.

  • Hydrocarbon: A compound formed from carbon and hydrogen atoms only.

  • Saturated Compound: A molecule where every carbon atom has four single covalent bonds. There are no double bonds present.

  • Homologous Series: A group of organic compounds that have similar properties, react in a similar way, and follow the same general formula.

2. The First Four Alkanes

You need to know the names and formulas of the first four members of the series:

  1. Methane: CH₄ (1 carbon atom)

  2. Ethane: C₂H₆ (2 carbon atoms)

  3. Propane: C₃H₈ (3 carbon atoms)

  4. Butane: C₄H₁₀ (4 carbon atoms)

3. General Formula for Alkanes

The general formula for the entire alkane series is CₙH₂ₙ₊₂.

  • n represents the number of carbon atoms.

  • To find the number of hydrogens, multiply the number of carbons by 2 and then add 2.

  • Example: For Octane (8 carbons), $n = 8$. The number of hydrogens is $(2 \times 8) + 2 = 18$. Molecular formula: C₈H₁₈.

4. Properties of Carbon

Carbon is essential for making large compounds because each atom can form four strong bonds. In alkanes, these bonds are always single. If you were to add a double bond, the molecule would no longer be an alkane; it would be an alkene.

5. Summary Checklist

  • Alkanes are saturated (single bonds only).

  • They grow by one carbon and two hydrogens (CH₂) each time.

  • They follow the formula CₙH₂ₙ₊₂.

  • Hydrocarbons must contain only carbon and hydrogen.