Atoms & the Nucleus
Year 7 ⚛️ Particles & Structure Describe the basic structure of an atom: nucleus, protons and electrons.
⚛️ The Atom
Everything is made of atoms. An atom is the smallest particle of an element that still has the chemical properties of that element.
Atoms are incredibly tiny — about 0.1 nm (1 × 10⁻¹⁰ m) in diameter. A single grain of sand contains billions of atoms.
🔬 Inside the Atom
An atom has a tiny, dense nucleus at the centre, surrounded by electrons arranged in shells (orbits).
| Subatomic particle | Location | Charge | Relative mass |
|---|---|---|---|
| Proton | Nucleus | +1 | 1 |
| Neutron | Nucleus | 0 | 1 |
| Electron | Shells (orbitals) | −1 | ~0 (1/1840) |
An atom is neutral because the number of protons = number of electrons.
🔢 Atomic Number & Mass Number
Key Definitions
$$\text{Atomic number (Z)} = \text{number of protons}$$
$$\text{Mass number (A)} = \text{protons} + \text{neutrons}$$
$$\text{Neutrons} = A - Z$$Carbon: Z = 6, A = 12 → 6 protons, 6 neutrons, 6 electrons.
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Interactive Demonstration — Atoms & the Nucleus
⚛️ Atom Builder
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