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John discovered that certain gases could only be combined in certain proportions. The experiments built upon two theories that had emerged near the end of the 18th century which dealt with chemical reactions.
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Thomson discovered the electron.
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Millikan discovered it was best to use an oil with an extremely low vapor pressure, such as one designed for use in a vacuum apparatus. Conducted the oil drop experiment.
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Rutherford discovered the nucleus. Experiment called the gold foil experiment.
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Bohr proposed his quantized shell model of the atom to explain how electrons can have stable orbits around the nucleus.
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Chadwick discovered the neutron. Chadwick put a piece of beryllium in a vacuum chamber with some polonium. The polonium emitted alpha rays, which struck the beryllium. When struck, the beryllium emitted the mysterious neutral rays.
