Group 7 — AQA GCSE Chemistry
Test yourself on Group 7 with AQA GCSE practice questions.
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Group 7 explained
Group 7 halogens exist as diatomic molecules.
Read the full explanation
Their relative molecular mass increases as you descend from fluorine to iodine because each atom has more protons and neutrons. As the molecules get larger, the intermolecular forces between them become stronger. More energy is therefore needed to overcome these intermolecular forces, so melting point and boiling point rise steadily down the group. For example, fluorine and chlorine are gases at room temperature, bromine is a liquid, and iodine is a solid. The trend in melting and boiling points is explained entirely by the strength of the intermolecular forces, not by the covalent bonds within the molecules.
Your focus
- Describe the trend in relative molecular mass, melting point and boiling point down Group 7.
- Explain the trend in terms of intermolecular forces between diatomic molecules.
- Use the trend to predict the physical state or relative melting point of a halogen from its position in the group.
Group 7 exam tips
Marking Points
- Group 7 elements are diatomic molecules, so relative molecular mass increases down the group as atomic number increases.
- Larger molecules have stronger intermolecular forces between them.
- Stronger intermolecular forces require more energy to overcome, so melting point and boiling point increase down the group.
- The trend is a physical property trend explained by intermolecular forces, not by the strength of the covalent bonds within each molecule.
- State symbols at room temperature change from gas to liquid to solid: fluorine and chlorine are gases, bromine is a liquid, iodine is a solid.
Examiner Tips
- 💡Link each property to the structure and bonding explanation: larger molecules, stronger intermolecular forces, more energy needed to melt or boil.
- 💡Use the correct comparison language, such as higher, lower, stronger and weaker, rather than vague words like bigger or more.
- 💡When asked to predict a trend, refer to the position in Group 7 and the change in intermolecular forces rather than memorising colours alone.
Common Mistakes
- Saying that melting point increases because the covalent bonds get stronger; the correction is that intermolecular forces between molecules get stronger, while covalent bonds within molecules do not break during melting.
- Confusing relative molecular mass with relative atomic mass; the correction is that halogens are diatomic, so relative molecular mass is twice the relative atomic mass for each element.
- Claiming that all halogens are gases at room temperature; the correction is that bromine is a liquid and iodine is a solid under standard conditions.