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This lesson covers the structure of the atom, the properties of subatomic particles, atomic number, mass number and isotopes. This is part of the AQA GCSE Combined Science Trilogy specification (8464, section 6.4.1 — Atoms and Isotopes).
Every atom consists of a small, dense nucleus at the centre, surrounded by electrons orbiting in shells (energy levels).
| Part of the atom | Contains | Charge | Relative mass |
|---|---|---|---|
| Nucleus | Protons and neutrons | Positive (due to protons) | Nearly all the mass of the atom |
| Electron shells | Electrons | Negative | Very little mass |
| Particle | Relative charge | Relative mass | Location |
|---|---|---|---|
| Proton | +1 | 1 | Nucleus |
| Neutron | 0 | 1 | Nucleus |
| Electron | −1 | Very small (≈ 1/1836) | Shells around the nucleus |
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