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Atomic structure

1. The mass number of an atom is the number of protons and neutrons

2. The nucleus is made of protons and neutrons and is at the centre of the atom

3. The first electron shell can only have two atoms

   • The next few electron shells hold up to eight electrons

4. Electrons are negatively charged

5. Protons are positively charged

6. Neutrons are neutrally charged

7. An electron's mass is 1

8. The number of electrons is equal to the number of protons and neutrons