Alkenes
Use this landing page to move between the alkene revision pages for Cambridge International AS Level Chemistry Topic 14.2. The bonding and isomerism of alkenes are covered in Topic 13 and polymers in Topic 20, so those pages are linked here as well.
Choose an Alkenes Page
Alkenes are unsaturated hydrocarbons containing a carbon-carbon double bond. These pages separate the topic into how alkenes are made, their bonding and isomerism, the electrophilic addition mechanism, their reactions, and the polymers formed from them.
Key idea: The C=C double bond contains a σ bond and a π bond. The electron-rich π bond makes alkenes react with electrophiles, and the same bond opens up when alkene monomers join in addition polymerisation.
Producing Alkenes
Elimination from halogenoalkanes with ethanolic NaOH, dehydration of alcohols and cracking of alkanes (14.2.1).
Start revisingAlkene Bonding
The σ and π bonds of the C=C double bond, sp2 hybridisation and the planar alkene (Topic 13.3).
Start revisingGeometric Isomerism
Restricted rotation about the C=C bond and geometrical (cis/trans) isomerism (Topic 13.4).
Start revisingElectrophilic Addition Mechanism
How electrophiles attack the π bond, carbocation intermediates, the inductive effect and Markovnikov addition (14.2.4, 14.2.5).
Start revisingMarkovnikov Addition
Understand the inductive effect of alkyl groups, carbocation stability and why HBr adds to propene to give mainly 2-bromopropane.
Start revisingReactions of Alkenes
Addition of hydrogen, halogens, hydrogen halides and steam, the bromine water test and oxidation by KMnO4 (14.2.2, 14.2.3).
Start revisingPolymerisation Reactions
Addition polymerisation of ethene, propene and chloroethene, repeat units and monomers (14.2.2, Topic 20).
Start revisingPolymer Waste
The difficulty of disposing of poly(alkene)s: non-biodegradability and harmful combustion products (Topic 20).
Start revisingHow to Use These Pages
Start with producing alkenes so you know where they come from, then revise alkene bonding and geometric isomerism in Topic 13. Move on to the electrophilic addition mechanism before the individual reactions, and finish with polymerisation and polymer waste in Topic 20.
Exam focus: Be able to state reagents and conditions for making alkenes, explain alkene reactivity using the π bond, draw the mechanisms for bromine with ethene and hydrogen bromide with propene, predict the major product using carbocation stability, and describe both the cold dilute and hot concentrated reactions with acidified KMnO4.
Copyright notice: This revision page, including its written explanations, layout and teaching sequence, is produced for Online Learning System by Dr. Mohammed Al-Fatah. It is intended for student revision and may not be copied, redistributed or republished without permission.
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