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AQA A Level Chemistry

3.2.3
Group 7 (17)

Section 3.2.3 covers the trends in electronegativity and boiling point of the halogens, their oxidising ability shown by displacement reactions, the reducing ability of the halide ions shown by their reactions with concentrated sulfuric acid, the acidified silver nitrate test and the ammonia follow-up, and the reactions of chlorine with water and with cold dilute sodium hydroxide, including the use of chlorine in water treatment.

Exam Paper
Paper 1 & 3
7405/1 and 7405/3
Specification Points
3.2.3.1 – 3.2.3.2
12 statements
Topic Parts
4 pages
Revision notes available
Exam Board
AQA
7405 (2015 onwards)

Revision Notes

Work through 3.2.3 Group 7 (17) in a structured sequence.

F₂ to I₂
Halogen
Trends
1
Available

Trends in the Halogens

The trends in Group 7 (17): states, colours, boiling points, electronegativity, reactivity and predictions for fluorine and astatine.

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Displacement
Oxidising
Agents
2
Available

Halogens as Oxidising Agents

The halogens as oxidising agents: displacement reactions, colours in water and cyclohexane, reactions with metals and hydrogen, and the reactivity trend.

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Water and bleach
Chlorine
Reactions
3
Available

Disproportionation Reactions of Chlorine

The disproportionation of chlorine with water and with cold and hot alkali, bleach, water treatment and analogous halogen reactions.

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Cl⁻, Br⁻, I⁻
Halide
Ions
4
Available

Halide Ions: Reducing Agents and Tests

Halide ions: reducing power with concentrated sulfuric acid, the acidified silver nitrate test and ammonia, and the hydrogen halides with ammonia and water.

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Specification Coverage

3.2.3 Group 7 (17), the Halogens – AQA A Level Chemistry

The following AQA specification points outline the knowledge and skills students are expected to demonstrate. Wording follows the AQA A Level Chemistry (7405) specification.

3.2.3.1 Trends in properties

i
The trend in electronegativity of the halogens down the group, and its explanation.
ii
The trend in boiling point of the halogens, explained in terms of their structure and bonding.
iii
The trend in oxidising ability of the halogens down the group, including displacement reactions of halide ions in aqueous solution.
iv
The trend in reducing ability of the halide ions, including the reactions of solid sodium halides with concentrated sulfuric acid.
v
The use of acidified silver nitrate solution to identify and distinguish between halide ions.
vi
The trend in solubility of the silver halides in ammonia.
vii
Explain why silver nitrate solution is used to identify halide ions, why it is acidified and why ammonia solution is added.

3.2.3.2 Uses of chlorine and chlorate(I)

i
The reaction of chlorine with water to form chloride ions and chlorate(I) ions.
ii
The reaction of chlorine with water to form chloride ions and oxygen.
iii
The use of chlorine in water treatment; the benefits to health outweigh its toxic effects.
iv
Society assesses the advantages and disadvantages when deciding if chemicals should be added to water supplies.
v
The reaction of chlorine with cold, dilute, aqueous NaOH and the uses of the solution formed.