History of Atoms

• John Dalton described atoms as tiny, hard spheres that could not be broken down into smaller parts.
• JJ Thompson came up with the Plum Pudding Model and his experiments of charge and mass showed atoms must contain smaller negatively charged particles - electrons.
• Rutherford's gold foil experiment showed that atoms were empty space as when he fired positively charged alpha particles at thin gold foil, most passed straight through. But, a few bounced back - most of the mass is in a central positive nucleus.
• Bohr suggested atoms had electrons contained in shells that can only exist in fixed orbits with a fixed energy.