Mass number A is protons plus neutrons

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Other lessons in this sub-strand

1. Atom, element and particle
2. The proton: positive, in the nucleus
3. The neutron: no charge, in the nucleus
4. The electron: negative, on shells
5. The nucleus is protons plus neutrons
6. Atomic number Z is the number of protons
7. Mass number A is protons plus neutrons
8. In a neutral atom, electrons equal protons
9. Energy levels fill 2, then 8, then 8, then 2
10. Arrangements of carbon, oxygen, sodium and chlorine
11. Dot diagrams: nucleus, rings, then dots
12. Metals: few outer electrons
13. Non-metals: more outer electrons, or a full shell
14. Practise the first 20: hydrogen to calcium