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1. Protons, Neutrons and Electrons For GCSE Science

2. Nucleus It is found in the middle of the atom It contains protons and neutrons It has a positive charge

3. Parts of an atom

4. Protons are heavy and have a positive charge Neutrons are heavy and are neutral Electrons are very light and are negatively charged

5. The number of protons = The number of electrons The number of neutrons = The mass number - protons

6. If you look at the periodic table at a Sodium Atom you will see its chemical symbol is Na. Mass Number The mass number = number of protons and neutrons. Na Atomic Number

7. For GCSE Chemistry Electrons occupy shells, orbits or energy levels. The lowest, inner shells are filled first Once the shell is full they go onto the next The first shell can have a maximum of 2 electrons The second shell can have a maximum of 8 electrons The third shell can have a maximum of 8 electrons

8. Atoms like full electronic shells. If the outer shell is not full, it makes them want to react.