AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Students should be able to: explain how the position of an element in the…
Full specification wording
The periodic table: Students should be able to: explain how the position of an element in the periodic table is related to the arrangement of electrons in its atoms and hence to its atomic number predict possible reactions and probable reactivity of elements from their positions in the periodic table. AQA GCSE Chemistry 8462. GCSE exams Jun
An element's position follows directly from its atomic number and electron arrangement.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 4 of 4
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
An element's position follows directly from its atomic number and electron arrangement. The atomic number gives the number of protons and, in a neutral atom, the number of electrons. Electrons fill shells in a regular way, so the outer-shell count determines the group and the number of occupied shells determines the period. For example, magnesium has atomic number 12, with two outer electrons in its third shell, placing it in Group 2 and Period 3. This position lets you predict behaviour: Group 1 metals lose one electron and react vigorously with water, Group 7 non-metals gain one electron and displace less reactive halogens, and Group 0 elements with full outer shells are unreactive.
What earns the marks
- Link atomic number to proton number and, for a neutral atom, electron number.
- Explain that the number of outer-shell electrons determines the group.
- Explain that the number of occupied electron shells determines the period.
- Use a named element to show the link between electron arrangement and position.
- Predict reactions or reactivity from group position, such as Group 1 reacting with water or Group 7 displacement.
- Recognise that reactivity trends within a group depend on distance of the outer electron from the nucleus and shielding.
Common mistakes and how to put them right
Using mass number instead of atomic number to find position.
Put it right by using proton number, which is the atomic number.
Placing an element in the wrong period by counting outer electrons rather than occupied shells.
Put it right by counting the shells that contain electrons.
Predicting identical reactivity for all group members.
Put it right by describing a trend, such as increasing reactivity down Group 1.
Exam tips
- Write the electron configuration first, then read group from outer electrons and period from shell count.
- When predicting a reaction, name the group, state the outer-electron behaviour and give the expected product or observation.
- Use correct ion notation with superscript signs, for example Mg²⁺ and O²⁻, when explaining electron loss or gain.
Try the lesson
The start of the The periodic table: Students should be able to: explain how the position of an element in the periodic table is related to the arrangement of electrons in its atoms and hence to its atomic number predict possible reactions and probable reactivity of elements from their positions in the periodic table. AQA GCSE Chemistry 8462. GCSE exams Jun lesson, made from checked teaching notes for this specification point.
Have a go first
An element is in Group 2 of the periodic table. How many electrons are in the outer shell of one of its atoms?
Listen
An element's position follows directly from its atomic number and electron arrangement. The atomic number gives the number of protons and, in a neutral atom, the number of electrons. Electrons fill shells in a regular way, so the outer-shell count determines the group and the number of occupied shells determines the period. For example, magnesium has atomic number 12, with two outer electrons in its third shell, placing it in Group 2 and Period 3. This position lets you predict behaviour: Group 1 metals lose one electron and react vigorously with water, Group 7 non-metals gain one electron and displace less reactive halogens, and Group 0 elements with full outer shells are unreactive. A strong answer earns marks for these points. Link atomic number to proton number and, for a neutral atom, electron number. Explain that the number of outer-shell electrons determines the group. Explain that the number of occupied electron shells determines the period. Use a named element to show the link between electron arrangement and position. A common slip: Using mass number instead of atomic number to find position. Instead, using proton number, which is the atomic number. Exam tip: Write the electron configuration first, then read group from outer electrons and period from shell count.
See it
Key words
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Atomic number
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Group
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Period
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Reactivity trends
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See every definition
- Atomic number
- Gives the number of protons and, in a neutral atom, the number of electrons.
- Group
- Determined by the number of outer-shell electrons in an atom.
- Period
- Determined by the number of occupied electron shells in an atom.
- Reactivity trends
- Within a group these depend on the distance of the outer electron from the nucleus and shielding.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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Test your understanding of The periodic table: Students should be able to: explain how the position of an element in the periodic table is related to the arrangement of electrons in its atoms and hence to its atomic number predict possible reactions and probable reactivity of elements from their positions in the periodic table. AQA GCSE Chemistry 8462. GCSE exams Jun
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