AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Students should be able to: explain how properties of the elements in…
Full specification wording
Group 7: Students should be able to: explain how properties of the elements in Group 7 depend on the outer shell of electrons of the atoms predict properties from given trends down the group.
The properties of Group 7 elements are determined by their outer shell electron configuration.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 7 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
The properties of Group 7 elements are determined by their outer shell electron configuration. Each halogen atom has seven electrons in its outer shell, so it needs to gain one electron to achieve a stable noble gas configuration. This explains why halogens form 1⁻ ions and why reactivity depends on how strongly the nucleus attracts an incoming electron. Down the group, atomic radius increases and shielding increases, so the attraction weakens and reactivity decreases.
What earns the marks
- Group 7 atoms have seven electrons in their outer shell and gain one electron to form a 1⁻ ion.
- The ease of gaining an electron depends on the attraction between the nucleus and the incoming electron, which is affected by atomic radius and shielding.
- Down the group, atomic radius and shielding increase, so the attraction for an incoming electron decreases and reactivity decreases.
- Physical properties such as melting point and boiling point increase down the group because intermolecular forces become stronger.
- Predictions should be based on trends in the group, such as a halogen lower down being less reactive and having a higher melting point.
Common mistakes and how to put them right
Saying halogens lose seven electrons to form ions.
Put it right: They gain one electron to form a 1⁻ ion.
Treating each property as an isolated fact rather than linking it to the outer shell electron configuration and atomic size.
Predicting that reactivity increases down the group because atomic number increases.
Put it right: Reactivity decreases because the outer shell electron is further from the nucleus and more shielded.
Exam tips
- Start explanations with the outer shell electron configuration and then link to the property being explained.
- When predicting a property, state the trend and use it to justify the prediction.
- Use correct chemical terminology, including 1⁻ ions, atomic radius, shielding and intermolecular forces.
Try the lesson
The start of the Group 7: Students should be able to: explain how properties of the elements in Group 7 depend on the outer shell of electrons of the atoms predict properties from given trends down the group. lesson, made from checked teaching notes for this specification point.
Have a go first
Why does the reactivity of Group 7 elements decrease as you go down the group?
Listen
The properties of Group 7 elements are determined by their outer shell electron configuration. Each halogen atom has seven electrons in its outer shell, so it needs to gain one electron to achieve a stable noble gas configuration. This explains why halogens form 1⁻ ions and why reactivity depends on how strongly the nucleus attracts an incoming electron. Down the group, atomic radius increases and shielding increases, so the attraction weakens and reactivity decreases. A strong answer earns marks for these points. Group 7 atoms have seven electrons in their outer shell and gain one electron to form a 1⁻ ion. The ease of gaining an electron depends on the attraction between the nucleus and the incoming electron, which is affected by atomic radius and shielding. Down the group, atomic radius and shielding increase, so the attraction for an incoming electron decreases and reactivity decreases. Physical properties such as melting point and boiling point increase down the group because intermolecular forces become stronger. A common slip: Saying halogens lose seven electrons to form ions. Instead, they gain one electron to form a 1⁻ ion. Exam tip: Start explanations with the outer shell electron configuration and then link to the property being explained.
Key words
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Outer shell electrons
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Reactivity and electron gain
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Group 7 trends
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Predicting properties
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See every definition
- Outer shell electrons
- Group 7 atoms have seven electrons in their outer shell, so each needs to gain one electron to achieve a stable noble gas configuration.
- Reactivity and electron gain
- The ease of gaining an electron depends on the attraction between the nucleus and the incoming electron, which is affected by atomic radius and shielding.
- Group 7 trends
- Down the group, atomic radius and shielding increase, so the attraction for an incoming electron decreases and reactivity decreases.
- Predicting properties
- Predictions should be based on trends in the group, such as a halogen lower down being less reactive and having a higher melting point.
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