Overview
This lesson explains the structure, formulas, and properties of alkanes, alkenes, and alkynes, focusing on their classification as hydrocarbons and on the concepts of saturated and unsaturated compounds.
Alkanes
- Alkanes are hydrocarbons with only single bonds between carbon atoms.
- They belong to a homologous series—a group of compounds with similar properties and general formulas.
- The general formula for alkanes is CₙH₂ₙ₊₂.
- Example: For 5 carbons, C₅H₁₂; for 9 carbons, C₉H₂₀.
- Alkanes are called “saturated” because each carbon forms four bonds, and no more atoms can be added.
Alkenes
- Alkenes are hydrocarbons with at least one double bond between carbons.
- Their general formula is CₙH₂ₙ (for molecules with only one double bond).
- Example: C₃H₆ and C₄H₈.
- Double bonds mean alkenes are “unsaturated”—more atoms (like hydrogen) can be added by breaking the double bond.
Alkynes
- Alkynes are hydrocarbons with at least one triple bond between carbons.
- Their general formula is CₙH₂ₙ₋₂.
- Example: C₄H₆ and C₃H₄.
- Like alkenes, alkynes are “unsaturated” because more atoms can be added if triple bonds are broken.
Saturated vs. Unsaturated
- Saturated compounds (e.g., alkanes) cannot accept more atoms because every carbon has four single bonds.
- Unsaturated compounds (alkenes and alkynes) can accept more atoms due to double or triple bonds.
Key Terms & Definitions
- Homologous series — a group of compounds sharing a general formula and similar properties.
- Hydrocarbon — a molecule made of only carbon and hydrogen.
- Saturated — all carbon bonds are single; no more atoms can be added.
- Unsaturated — contains double or triple bonds; more atoms can be added.
Action Items / Next Steps
- Practice identifying alkanes, alkenes, and alkynes using their general formulas.
- Review the definitions of saturated and unsaturated compounds.
- Prepare for upcoming lessons on naming hydrocarbons.