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AQA A Level Chemistry

3.3.3
Halogenoalkanes

Section 3.3.3 covers the polar carbon–halogen bond, nucleophilic substitution with hydroxide, cyanide and ammonia with their mechanisms, the effect of bond enthalpy on the rate of hydrolysis, elimination and its mechanism with the reagent acting as both nucleophile and base, and the role of chlorine radicals from CFCs in the depletion of the ozone layer.

Exam Paper
Paper 2
7405/2
Specification Points
3.3.3.1 – 3.3.3.3
3 sections covered
Sub-topics
6 lessons
Revision notes available
Exam Board
AQA
7405 (2015 onwards)

Revision Notes

6 revision notes, in the order the specification teaches them.

A nucleophile approaching a halogenoalkane
1

Reaction Types, Mechanisms and Nucleophiles

Organic reaction types and mechanisms: addition, elimination, substitution, oxidation, reduction, hydrolysis, polymerisation, curly arrows, heterolytic fission, electrophiles, nucleophiles and bond polarity.

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A halogen on a carbon chain
2

Halogenoalkanes: Naming, Classification and the C–X Bond

Halogenoalkanes: nomenclature and formulae, primary, secondary and tertiary, the polar carbon–halogen bond, bond enthalpies and uses.

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A hydroxide group replacing a halogen on a carbon atom
3

Nucleophilic Substitution Reactions

Nucleophilic substitution of halogenoalkanes: hydroxide, water, ammonia and cyanide as nucleophiles, conditions, products and the curly-arrow mechanism.

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A halogenoalkane losing a small molecule to form a double bond
4

Elimination Reactions of Halogenoalkanes

Elimination of halogenoalkanes: ethanolic KOH, hydroxide as a base, alkene products and isomers, substitution versus elimination.

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Three carbon to halogen bonds getting longer and weaker
5

Rates of Hydrolysis and Bond Enthalpy

Rates of hydrolysis of halogenoalkanes: the silver nitrate experiment, precipitate colours, bond enthalpy trend for C–Cl, C–Br and C–I, and primary, secondary and tertiary comparison.

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An ozone layer above the earth with a breaking molecule
6

CFCs and the Ozone Layer

CFCs and the ozone layer: chlorine radicals, the equations for ozone decomposition, the catalytic cycle, legislation and HFC alternatives.

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Summary Map

Download, print and revise the reactions of this topic at a glance.

Summary maps

Download, print and revise the reactions of this topic at a glance.

Illustration of a summary map: compounds joined by reaction arrows
Summary map · PDF

Halogenoalkanes Map

AQA A Level Chemistry · 3.3.3 Halogenoalkanes

Every reaction on one A4 page: reagents, conditions and reaction type for each arrow, colour coded, with the key tests.

Download the map4 reactions · A4 landscape · print ready
Illustration of a summary map: compounds joined by reaction arrows
Summary map · PDF

Halogenoalkanes Summary Map

AQA A-level Chemistry · 3.3.3 Halogenoalkanes

The whole section on one A4 page: names, classes and nucleophiles, substitution by hydroxide, water, ammonia and cyanide, elimination, rates of hydrolysis, and ozone and CFCs.

Download the map6 key ideas + a data table · A4 portrait · print ready

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Revision Game

Match reagents to products, free, with your board's reagents and conditions.

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Revision Game: Halogenoalkanes

Turn the cards over two at a time: match reagents to what they make, and find how each product is made.

A free memory game on the reactions in this topic, with your board's reagents, conditions and spec points.

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Specification

Every specification point in this topic, in the exam board's own words. Rate how confident you are with each one.

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3.3.3.1

  1. i

    know that halogenoalkanes contain polar bonds

    Revise
  2. ii a

    know that halogenoalkanes undergo substitution reactions with OH-

    Revise
  3. ii b

    know that halogenoalkanes undergo substitution reactions with CN-

    Revise
  4. ii c

    know that halogenoalkanes undergo substitution reactions with NH3

    Revise
  5. iii a

    outline the nucleophilic substitution mechanism of halogenoalkanes with OH-

    Revise
  6. iii b

    outline the nucleophilic substitution mechanism of halogenoalkanes with CN-

    Revise
  7. iii c

    outline the nucleophilic substitution mechanism of halogenoalkanes with NH3

    Revise
  8. iv

    explain why the carbon-halogen bond enthalpy influences the rate of reaction

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3.3.3.2

  1. i

    know that a halogenoalkane can undergo concurrent substitution and elimination reactions (eg 2-bromopropane with potassium hydroxide)

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  2. ii

    explain the role of the reagent as both nucleophile and base in elimination reactions

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  3. iii a

    outline substitution mechanisms of halogenoalkanes

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  4. iii b

    outline elimination mechanisms of halogenoalkanes

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3.3.3.3

  1. i

    know that ozone in the upper atmosphere is beneficial because it absorbs ultraviolet radiation

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  2. ii

    know that chlorine atoms are formed in the upper atmosphere when ultraviolet radiation causes C-Cl bonds in CFCs to break

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  3. iii

    know that chlorine atoms catalyse the decomposition of ozone and contribute to the hole in the ozone layer

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  4. iv a

    use the equation Cl + O3 -> ClO + O2 to explain chlorine-catalysed decomposition of ozone

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  5. iv b

    use the equation ClO + O3 -> 2O2 + Cl to explain chlorine-catalysed decomposition of ozone

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  6. v

    appreciate that scientific evidence provided by different research groups led to legislation to ban the use of CFCs and that chemists have developed alternative chlorine-free compounds

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