Summary
Alkenes are unsaturated hydrocarbons with at least one carbon-carbon double bond, making them more reactive than alkanes. They can undergo various reactions such as electrophilic addition and polymerization.
- Alkenes — unsaturated hydrocarbons with a C=C bond. Example: Ethene (C2H4) is the simplest alkene.
- Sigma Bonds (σ) — bonds formed by end-to-end overlap of orbitals. Example: Found in the single bonds of ethene.
- Pi Bonds (π) — bonds formed by sideways overlap of p orbitals. Example: The second bond in the C=C double bond of ethene.
- Geometric Isomerism — isomers with different spatial arrangements around a C=C bond. Example: Cis/trans isomers like cis-2-butene and trans-2-butene.
- Electrophilic Addition — a reaction where an electrophile adds to a double bond. Example: Bromine adds to ethene to form 1,2-dibromoethane.
- Addition Polymerization — process where monomers with C=C bonds form polymers. Example: Ethene polymerizes to form polyethylene.
Exam Tips
Key Definitions to Remember
- Alkenes are hydrocarbons with at least one C=C bond.
- Sigma bonds are formed by end-to-end overlap of orbitals.
- Pi bonds are formed by sideways overlap of p orbitals.
Common Confusions
- Confusing sigma and pi bonds in alkenes.
- Misidentifying cis/trans isomers.
Typical Exam Questions
- What is the general formula for alkenes? CnH2n
- How does bromine react with alkenes? Through electrophilic addition to form dibromo compounds.
- What is the product of ethene polymerization? Polyethylene
What Examiners Usually Test
- Understanding of electrophilic addition mechanisms.
- Ability to identify and name geometric isomers.
- Knowledge of polymerization processes and their applications.