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Democritus proposed the existence of atoms. Due to the limited technology at the time, his idea could not be tested.
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In 1804, Dalton then developed his theory of atoms and matter. After experiments in chemistry, Dalton was able to support his hypothesis with evidence.
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JJ Tomson discovered the electron. He experimented using electric charges in cathode ray tubes.
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Rutherford developed the planetary model of the atom. Rutherford experimented using alpha particles fired at thin gold foil. An early prototype of a 'Geiger counter' was used to measure results.
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Bohr developed a model of the atom. Using mathematical models and laws of quantum physics, Bohr developed his updated model.
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James Chadwick discovered the neutron. He experimented using kinematics and accurate measurements, which lead him to discover the neutron.
