Alkanes, Alkenes and Hydrocarbons
Hydrocarbon properties, combustion, cracking, radical substitution, electrophilic addition, polymerisation and the environmental implications of fuels.
How to study A-level Chemistry
Represent the species and process correctly, conserve atoms, charge and energy, calculate with units, then test the result against observations and chemical evidence.
Core concepts
Concept 1
Alkanes are relatively unreactive non-polar hydrocarbons but undergo combustion, cracking and radical substitution.
Exam cue: Use initiation, propagation and termination stages for radical substitution.
Concept 2
The electron-rich π bond makes alkenes susceptible to electrophilic addition and addition polymerisation.
Exam cue: Show curly arrows from electron pair or bond to the accepting species.
Concept 3
Fuel and feedstock choices involve energy, atom economy, emissions, resource availability and process conditions.
Exam cue: Distinguish complete combustion products from those formed with limited oxygen.
Risk pitfalls and guardrails
Drawing a curly arrow from a positive charge rather than electron density.
Guardrail: Do not substitute a memorised equation, mechanism or trend until you have identified the species, conditions and chemical model required.
Using heterolytic arrows in a radical mechanism.
Guardrail: Do not substitute a memorised equation, mechanism or trend until you have identified the species, conditions and chemical model required.
Assuming addition polymerisation releases a small molecule.
Guardrail: Do not substitute a memorised equation, mechanism or trend until you have identified the species, conditions and chemical model required.
Memory anchors
Homolytic Fission
A covalent bond breaks with one electron going to each atom.
Radical
A radical is a species containing an unpaired electron.
Electrophile
An electrophile accepts an electron pair.
Electrophilic Addition
An electrophile attacks the electron-rich π bond before addition completes.
Addition Polymer
An addition polymer forms when alkene π bonds open and monomers join without a small by-product.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
Why are alkanes relatively unreactive toward many polar reagents?
Which equation is complete combustion of ethane?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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