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- Understand the history of atomic structure - State the relative charges and approximate relative masses of protons, neutrons and electrons - Define proton number (atomic number) as the number of protons in the nucleus of an atom - Define nucleon number (mass number) as the total number of protons and neutrons in the nucleus of an atom - Use proton number and the simple structure of atoms to explain the basis of the Periodic Table, with special reference to the elements of proton number 1 to 20