Group 7: The Halogens
Recap Group 7: The Halogens for GCSE Chemistry with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. A more reactive halogen displaces a less reactive one from its salt, and reactivity decreases down Group 7.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Group 7 elements, the halogens, are non-metals that exist as molecules made of pairs of atoms, such as Cl₂. They all have seven electrons in their outer shell.
Going down the group the melting and boiling points increase, and the relative molecular mass increases. Reactivity decreases down the group — the opposite trend to group 1, and the distinction is examined regularly.
Reactivity decreases because the outer shell is further from the nucleus with more shielding, so an electron is gained less easily. A more reactive halogen can displace a less reactive one from an aqueous solution of its salt, which is the basis of displacement reactions.
Revision notes
Properties and trends
Halogens exist as diatomic molecules such as Cl₂ and have seven outer shell electrons.
Going down the group, melting and boiling points increase and relative molecular mass increases. Reactivity decreases.
Why reactivity decreases
Going down the group, the outer shell is further from the nucleus and there is more shielding.
The attraction that pulls in an additional electron is therefore weaker, so an electron is gained less easily and the halogen is less reactive. This is the opposite reasoning to group 1, where an electron is lost.
Displacement reactions
A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.
For example, chlorine displaces bromine from potassium bromide: chlorine + potassium bromide → potassium chloride + bromine. The solution turns orange as bromine is formed.
Key points
- Halogens exist as molecules of two atoms.
- They have seven outer shell electrons.
- Melting and boiling points increase down the group.
- Reactivity decreases down the group.
- An electron is gained less easily further down.
- A more reactive halogen displaces a less reactive one.
Worked examples
Example 1
Explain why reactivity decreases down group 7. [3 marks]
Model answer
Going down the group, the outer shell is further from the nucleus (1 mark) and there is more shielding from inner electron shells (1 mark). The attraction pulling in an additional electron is therefore weaker, so an electron is gained less easily (1 mark).
Example 2
Write the word equation for the reaction between chlorine and potassium bromide. [2 marks]
Model answer
Chlorine + potassium bromide → potassium chloride + bromine. Correct reactants (1 mark). Correct products (1 mark).
Example 3
Explain why iodine cannot displace chlorine from sodium chloride. [2 marks]
Model answer
Iodine is below chlorine in group 7, so it is less reactive (1 mark). A less reactive halogen cannot displace a more reactive one from a solution of its salt, so no reaction occurs (1 mark).
Common mistakes
Saying reactivity increases down group 7.
It decreases — the opposite trend to group 1.
Writing halogens as single atoms.
They exist as molecules of two atoms, such as Cl₂.
Explaining the trend as losing electrons.
Halogens gain an electron, so the reasoning is about attraction pulling one in.
Predicting a displacement that cannot happen.
Only a more reactive halogen displaces a less reactive one.
Exam tips
- Contrast the group 7 trend directly with group 1.
- Say gaining an electron, not losing, when explaining reactivity.
- Write halogen formulae as diatomic molecules.
- Check the order of reactivity before predicting a displacement.
Key terms
- Halogen
- A group 7 non-metal with seven outer shell electrons.
- Diatomic
- Existing as molecules of two atoms.
- Displacement
- A reaction where a more reactive element takes the place of a less reactive one.
- Halide
- A compound formed between a halogen and a metal.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.