AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
These periodic properties can be explained in terms of the atomic…
Full specification wording
Key ideas: these periodic properties can be explained in terms of the atomic structure of the elements
Periodic trends arise from atomic structure: the number of protons, the number of electron shells and the number of electrons in the outer shell.
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- Point 12 of 26
Study notes
From the checked teaching notes for this specification point.
The idea
Periodic trends arise from atomic structure: the number of protons, the number of electron shells and the number of electrons in the outer shell. Across a period, the nuclear charge increases while the outer shell stays the same, so atoms attract outer electrons more strongly; this helps explain changes in melting point and reactivity. Down a group, the number of occupied shells increases, so the outer electron is further from the nucleus and shielded by inner shells; this explains why Group 1 metals lose their outer electron more easily and become more reactive, while Group 7 halogens attract an extra electron less strongly and become less reactive. Noble gases have full outer shells, explaining their unreactivity.
For example: Sodium (2,8,1) and potassium (2,8,8,1) both have one outer electron, but potassium's outer electron is in a higher shell, so it is lost more easily.
What earns the marks
- Links an element's position to its number of protons and electron configuration.
- Explains that elements in the same group have the same number of outer-shell electrons, giving similar chemical properties.
- Explains that reactivity in Group 1 increases down the group because the outer electron is further from the nucleus and more shielded.
- Explains that reactivity in Group 7 decreases down the group because the outer shell is further from the nucleus, so attraction for an incoming electron is weaker.
- Explains noble gas unreactivity in terms of full outer electron shells.
- Uses a specific electron configuration, such as sodium 2,8,1 or chlorine 2,8,7, to support an explanation.
Common mistakes and how to put them right
Confusing group number with number of shells.
Put it right by stating group number equals outer-shell electrons for main-group elements, while period number equals shells occupied.
Saying shielding increases across a period.
Put it right by noting shielding is similar across a period while nuclear charge increases.
Claiming Group 7 reactivity increases down the group.
Put it right by explaining that increased distance and shielding weaken attraction for an incoming electron.
Exam tips
- Name the subatomic particles and shells involved, then link them to the trend in one clear causal chain.
- Use electron configurations such as 2,8,1 to show why elements in the same group behave similarly.
- For comparison questions, refer to both distance from the nucleus and shielding to explain the difference.
Try the lesson
The start of the Key ideas: these periodic properties can be explained in terms of the atomic structure of the elements lesson, made from checked teaching notes for this specification point.
Have a go first
Sodium is in Group 1 of the periodic table. Which statement explains why sodium is placed in Group 1?
Listen
Periodic trends arise from atomic structure: the number of protons, the number of electron shells and the number of electrons in the outer shell. Across a period, the nuclear charge increases while the outer shell stays the same, so atoms attract outer electrons more strongly; this helps explain changes in melting point and reactivity. Down a group, the number of occupied shells increases, so the outer electron is further from the nucleus and shielded by inner shells; this explains why Group 1 metals lose their outer electron more easily and become more reactive, while Group 7 halogens attract an extra electron less strongly and become less reactive. Noble gases have full outer shells, explaining their unreactivity. For example, sodium (2,8,1) and potassium (2,8,8,1) both have one outer electron, but potassium's outer electron is in a higher shell, so it is lost more easily. A strong answer earns marks for these points. Links an element's position to its number of protons and electron configuration. Explains that elements in the same group have the same number of outer-shell electrons, giving similar chemical properties. Explains that reactivity in Group 1 increases down the group because the outer electron is further from the nucleus and more shielded. Explains that reactivity in Group 7 decreases down the group because the outer shell is further from the nucleus, so attraction for an incoming electron is weaker. A common slip: Confusing group number with number of shells. Instead, stating group number equals outer-shell electrons for main-group elements, while period number equals shells occupied. Exam tip: Name the subatomic particles and shells involved, then link them to the trend in one clear causal chain.
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