4cOrganic Chemistry
Alkanes — Edexcel Linear - OL (Chemistry) Revision Notes & Topical Questions
5 min read 7 parts Lesson 3 of 18 1 quiz
Lesson summary
Alkanes Edexcel O Level Linear Chemistry notes: know the general formula for alkanesTertiary carbocations are most stable – major product.Poly(ethene) is unreactive – non-biodegradable.Incomplete combustion produces CO and soot.know the general formula for alkanesexplain why alka…
- Alkanes Edexcel O Level Linear Chemistry: what to do next
- Free radical
- Addition polymer
- Bromine water test
- Markovnikov’s rule
- Give / State / Name
Part 1 of 6Key ideas
Key ideas
Tertiary carbocations are most stable – major product.
Poly(ethene) is unreactive – non-biodegradable.
Incomplete combustion produces CO and soot.
Part 2 of 6Syllabus points
1
know the general formula for alkanes
2
explain why alkanes are classified as saturated hydrocarbons
3
understand how to draw the structural and displayed formulae for alkanes with up to five carbon atoms in the molecule, and to name the unbranched-chain isomers
4
describe the reactions of alkanes with halogens in the presence of ultraviolet radiation, limited to mono-substitution knowledge of reaction mechanisms is not required
Part 3 of 6Process & sequence
1
Initiation: Cl₂ → 2Cl• (UV).
2
Propagation: Cl• + CH₄ → HCl + •CH₃.
3
•CH₃ + Cl₂ → CH₃Cl + Cl•.
4
Termination: two radicals join.
- Alkene π electrons
- Attack δ+ Br
- Carbocation
- Br⁻ attacks
- Dibromoalkane
Part 4 of 6Summary
Summary
Alkenes decolourise bromine water.
Alkanes react with Cl₂ by free-radical substitution.
Part 5 of 6Keep going
Alkanes Edexcel O Level Linear Chemistry: what to do next
These Alkanes Edexcel O Level Linear Chemistry notes covered the key ideas, worked examples and exam technique for this topic. Check your Alkanes Edexcel O Level Linear Chemistry understanding with the practice questions below, then reread any Alkanes Edexcel O Level Linear Chemistry point you were unsure about before moving on.
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Previous lesson: 4b Crude oil — Notes
3
Next lesson: 4d Alkenes — Notes
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Official syllabus: Pearson Edexcel International GCSEs
Part 6 of 6Compare: Compare
| Feature | Alkanes | Alkenes | Reason | Reaction example | Conditions |
|---|---|---|---|---|---|
| Bonding | σ bonds only | σ + π (C=C) | π bond electron-rich | — | — |
| Reactivity | Low | High | Weak π bond | — | — |
| With halogens | Free-radical substitution | Electrophilic addition | — | CH₄ + Cl₂ → CH₃Cl + HCl | UV light |
| With H₂ | — | Addition → alkane | — | Ethene + H₂ → ethane | Ni catalyst, 150 °C |
| With H₂O (steam) | — | Addition → alcohol | — | Ethene → ethanol | H₃PO₄, 300 °C, 60 atm |
| With KMnO₄ | No reaction | Diol formed (cold) / cleavage (hot) | — | — | Acidified |
Key terms
Command terms
Command terms
Give / State / Name
Recall a fact; one idea per mark.
Define
Give the exact meaning using the specification keywords.
Describe
Give an account of what happens / the pattern in data, quoting values; no reasons needed.
Explain
Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.
Suggest
Use knowledge in a new context; more than one answer may be accepted.
Compare
Similarities and differences; each point must refer to both items.
Calculate
Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.
Discuss
Explore the issue from different angles and link the points.
Evaluate / Assess
Weigh strengths and weaknesses and reach a supported judgement.
Deduce
Draw a conclusion from the information given.
Justify
Support a statement/choice with evidence.
Exam technique
Keywords the mark scheme looks for in this lesson
Keywords the mark scheme looks for in this lesson
Alkane · Alkene · Free radical · Cracking · Addition polymer · Bromine water test · Markovnikov’s rule · Complete combustion
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.
How to get full marks (examiner guidance)
How to get full marks (examiner guidance)
Use specification keywords exactly (e.g. electronegativity, nucleophile, dynamic equilibrium, activation energy).
Link ideas
Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.
Use the information in the question
“discuss/evaluate” answers must use the data provided and match the number of marks.
Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.
Avoid vague words
“it”, “stuff”, “things”, “goes up”, “energy is made”. Name the substance and the process.
Do not extrapolate a graph line beyond the data or to zero unless asked.
Six-mark extended responses are marked on content AND a logical, linked line of reasoning.
Marked practiceQuizzes for this lesson
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