Alkenes

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.