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Democritus invented that basis of the atomic theory. His model was described as a round sphere with no proton, neutrons or electrons.
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Dalton hypothesized that the atoms that make up different elements could be distinguished by their differences in weight. The model was described as a round, hard sphere that had no oher smaller parts.
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Dalton discovered electrons and developed the mass spectrograph. His model was a sphere of matter in which electrons are positioned.
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Rutherford tested his theories using his gold foil experiment. He discovered the atomic nucleus. The model was described as a positive nucleus orbited by negative electrons (Plum Pudding model).
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Bohr explained how electrons have stable orbits around the nucleus (Quantized shell model).
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Chadwick discovered the neutron. His model was similar to Bohr's in that it contains protons witha nucleus orbitted by negatively charged electrons.
