Group 7: the halogens Edexcel International GCSE Science (Single Award) revision
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In plain words
Chlorine, bromine and iodine are a family of coloured, poisonous non-metals. They go around in pairs (Cl₂, Br₂, I₂). Each atom is one electron short of a full shell, so they are keen to grab one, and the higher up the group, the keener.
Three things to know
- At room temperature chlorine is a pale yellow-green gas, bromine a red-brown liquid and iodine a grey-black solid. Going down Group 7 (VII) they get darker, denser and less reactive.
- A more reactive halogen pushes a less reactive one out of its compounds: Cl₂ + 2KBr → 2KCl + Br₂. This is a displacement reaction.
- Each atom has seven outer electrons and gains one to form a 1− ion (a halide). Further down, the outer shell is further from the nucleus, so an extra electron is attracted less strongly.
Worked example
Chlorine is bubbled into potassium iodide solution. What happens?
- Chlorine is above iodine in the group, so it is more reactive.
- It displaces the iodine: Cl₂ + 2KI → 2KCl + I₂.
- The colourless solution turns brown as iodine forms.
Tips and tricks
- The trend runs the opposite way to Group 1: reactivity decreases down Group 7.
- Chlorine is the element; chloride is the ion. A displacement happens only if the element is more reactive than the one in the compound.
It lands in your notebook with its questions as flashcards.
Group 7: the halogens: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
How does reactivity change going down Group 7?
It gets harder to attract an extra electron.
What is bromine like at room temperature?
It is one of only two elements that are liquid at room temperature.
Which pair will react?
Only a more reactive halogen can displace a less reactive one.
Halogen molecules contain how many atoms?
They are diatomic: Cl₂, Br₂, I₂.
How many outer electrons does a halogen atom have?
They are in Group 7.
What is the charge on a halide ion?
The atom gains one electron.
Quiz
6 questions
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Worksheet
4 questions, 9 marks. Write your answers on paper, then check them.
Group 7: the halogens
Edexcel International GCSE Science (Single Award) 4SS0 · 9 marks · papermunch.org
Name ______________________________ Date ______________
State the physical state and colour of chlorine, bromine and iodine at room temperature.[3]
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Chlorine: pale yellow-green gas. Bromine: red-brown liquid. Iodine: grey-black solid.
Chlorine water is added to colourless potassium iodide solution. State what is seen and write the equation.[2]
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The solution turns brown. Cl₂ + 2KI → 2KCl + I₂.
Explain why there is no reaction when iodine is added to potassium bromide solution.[2]
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Iodine is less reactive than bromine, so it cannot displace it.
Astatine is below iodine in Group 7. Predict its state at room temperature and how its reactivity compares with iodine's.[2]
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A solid (dark in colour); less reactive than iodine.
Answers: Group 7: the halogens
- 1. Chlorine: pale yellow-green gas. Bromine: red-brown liquid. Iodine: grey-black solid.
- 2. The solution turns brown. Cl₂ + 2KI → 2KCl + I₂.
- 3. Iodine is less reactive than bromine, so it cannot displace it.
- 4. A solid (dark in colour); less reactive than iodine.