Electronic Structure
Revise Electronic Structure for GCSE Chemistry with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Electrons fill shells in the pattern 2, 8, 8 — for example chlorine is 2,8,7. Learn to draw the electronic structures of the first 20 elements.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Electrons occupy the lowest available energy levels, or shells, around the nucleus. The arrangement of electrons determines an element's chemical properties.
The first shell holds a maximum of 2 electrons, the second holds 8, and the third holds 8 for the elements required at GCSE. Electrons fill the innermost shell first before moving outwards.
The electronic structure is written as numbers separated by commas, such as 2,8,1 for sodium. The number of electrons in the outer shell equals the group number in the periodic table, and the number of occupied shells equals the period number.
Revision notes
Filling the shells
Electrons occupy the lowest available energy level first.
First shell: maximum 2 electrons. Second shell: maximum 8. Third shell: 8 for the elements required at GCSE. Only when a shell is full do electrons begin filling the next.
Writing electronic structures
Write the number of electrons in each shell separated by commas, starting from the innermost.
Sodium has 11 electrons, so its structure is 2,8,1. Chlorine has 17, giving 2,8,7. Argon has 18, giving 2,8,8.
Link to the periodic table
The number of outer shell electrons equals the group number.
The number of occupied shells equals the period number. Sodium, with structure 2,8,1, is in group 1 and period 3. This link is what makes the periodic table predictive.
Key points
- Electrons occupy the lowest available energy level first.
- The first shell holds a maximum of 2 electrons.
- The second and third shells hold 8 each at GCSE.
- Electronic structures are written as 2,8,1.
- Outer shell electrons equal the group number.
- Occupied shells equal the period number.
Worked examples
Example 1
Write the electronic structure of an atom with 12 electrons. [2 marks]
Model answer
2,8,2. The first shell holds 2 electrons and the second holds 8 (1 mark), leaving 2 electrons in the third shell (1 mark).
Example 2
An element has the electronic structure 2,8,7. State its group and period. [2 marks]
Model answer
Group 7, because there are 7 electrons in the outer shell (1 mark). Period 3, because there are 3 occupied shells (1 mark).
Example 3
Explain why elements in the same group have similar chemical properties. [2 marks]
Model answer
Elements in the same group have the same number of electrons in their outer shell (1 mark), and it is the outer shell electrons that determine how an atom reacts (1 mark).
Common mistakes
Putting more than 2 electrons in the first shell.
The first shell holds a maximum of 2.
Forgetting the commas.
The structure is written 2,8,1 — the commas separate the shells.
Confusing group and period.
Group comes from outer shell electrons; period from the number of shells.
Filling an outer shell before an inner one.
Electrons always occupy the lowest available energy level first.
Exam tips
- Fill shells in order: 2, then 8, then 8.
- Count the last number for the group and the number of digits for the period.
- Explain similar properties through outer shell electrons.
- Check the digits add up to the total number of electrons.
Key terms
- Energy level
- A shell in which electrons are arranged.
- Electronic structure
- The arrangement of electrons in shells, such as 2,8,1.
- Group
- A vertical column of the periodic table.
- Period
- A horizontal row of the periodic table.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.