The structure of an atom — AQA GCSE Physics
Test yourself on The structure of an atom with AQA GCSE practice questions.
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The structure of an atom explained
An atom has a radius of roughly 1 × 10⁻¹⁰ m, while its nucleus is smaller than 1 × 10⁻¹⁴ m, so the nucleus occupies less than one ten-thousandth of the atomic radius.
Read the full explanation
Scaled up, if an atom were a sports stadium the nucleus would be a pea at the centre, and everything else is empty space through which the electrons move. Despite that tiny size, the nucleus holds nearly all the mass, because protons and neutrons are each about two thousand times heavier than an electron. Alpha particle scattering supplies the evidence for both claims: most alpha particles passed straight through the foil, but a few rebounded from something small, massive and positively charged.
Your focus
- State the approximate radius of an atom and of a nucleus, and calculate the ratio between them.
- Explain why almost all the mass of an atom lies in its nucleus, referring to the masses of protons, neutrons and electrons.
- Interpret the alpha scattering results as evidence that the atom is mostly empty space with a tiny massive centre.
The structure of an atom exam tips
Marking Points
- one mark for the radius of the nucleus being less than 1/10 000 of the radius of the atom
- one mark for quoting about 1 × 10⁻¹⁰ m for the atom and about 1 × 10⁻¹⁴ m or smaller for the nucleus
- one mark for stating that the mass of the atom is concentrated in the nucleus
- one mark for stating that most of the atom is empty space
Examiner Tips
- 💡Learn the two orders of magnitude, 10⁻¹⁰ m and 10⁻¹⁴ m; comparison questions often just want these.
- 💡Answer mass questions with the phrase concentrated in the nucleus, which is the wording the mark scheme uses.
- 💡If the question asks about the atom being mostly empty space, link it to alpha particles passing straight through.
Common Mistakes
- quoting 1/10 000 as a ratio of masses rather than of radii
- giving the nucleus a radius of 10⁻¹⁰ m, which is the size of the whole atom
- saying the electrons account for most of the mass because there are several of them
- claiming the nucleus is massive because it is large