Describe the structure of an atom, including the relative charges and masses of the particles found inside it.

AQA A-Level Physics (7408) — 3.2.1 Particles · Describe · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (5 marks)

An atom consists of a central nucleus surrounded by electrons.
1. The nucleus contains protons and neutrons.
2. Protons carry a relative charge of +1.
3. Neutrons carry a relative charge of 0.
4. Electrons orbit the nucleus and have a relative charge of –1.
5. Protons and neutrons each have a relative mass of about 1, while electrons have a negligible mass (≈1/1836 of a proton).

Examiner tips

Use the exact terms ‘nucleus’, ‘protons’, ‘neutrons’, ‘electrons’, ‘relative charge’, ‘relative mass’.
Show the charge signs (+1, 0, –1) and the mass comparison clearly.
Keep the answer concise – 5 points, one per bullet.

Common mistakes

Confusing electron charge sign or omitting the charge of the neutron.
Using ‘very small’ instead of the specific mass ratio 1/1836.

Mark scheme (5 marks)

The atom has a nucleus at its centre (with electrons surrounding/orbiting it)
The nucleus contains protons and neutrons
Proton has a relative charge of +1 and neutron has a relative charge of 0
Electron has a relative charge of −1
Protons and neutrons each have a relative mass of 1 (approximately), whereas electrons have a negligible / very small mass (or relative mass of 1/1836 / approximately 0)

Key terms in this question

relative charge