Atoms
Science, Chemistry. Usually met in years 8 to 11.
Work out protons, neutrons and electrons from atomic and mass numbers, shell patterns and ions.
What you practise
- Protons from the atomic number
- Neutrons from the mass number
- Electron shells and ions
Ends with the number of electrons in an ion. Practice moves up a level when a round goes well and down when it does not.
Sample questions
Each sample comes with the method and the reason every wrong option is wrong. Real practice rounds are ten questions at your level.
Sample question, level 2 of 5
Neon (Ne) has atomic number 10 and mass number 20. How many neutrons does one atom have?
- 11
- 10
- 30
- 12
- 20
Show the answer and method
Answer: B, 10
The method: Neutrons = mass number − atomic number = 20 − 10 = 10.
Why the other options are wrong:
- A, 11: Close, but check the subtraction.
- C, 30: The two numbers were added instead of subtracted.
- D, 12: Close, but check your working: this is a small slip away from the answer.
- E, 20: This is the mass number: the protons plus the neutrons.
Sample question, level 4 of 5
An atom of sulfur (S) has 16 electrons, arranged in shells that hold 2, then 8, then 8, then 2. How many electrons are in its outer shell?
- 7
- 16
- 6
- 10
- 5
Show the answer and method
Answer: C, 6
The method: The electrons fill the shells in order: 2,8,6. The last shell has 6 electrons.
Why the other options are wrong:
- A, 7: Close, but check how the shells fill: 2, then 8, then 8.
- B, 16: This is the total number of electrons, not the number in the outer shell.
- D, 10: This is the number of electrons in the inner shells.
- E, 5: Close, but check how the shells fill: 2, then 8, then 8.
See where this fits: GCSE science with AQA and Key Stage 3.
Related topics: States of matter, Formula mass, Moles.
