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Democritus believed evrything is made up of atoms
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Lavoisier came up with the law of conversion of mass and found oxygen
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Proust discovered that chemical compunds consist of elements
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Dalton discovered that All matter consists of tiny particles. Atoms are indestructible and unchangeable. Elements are characterized by the mass of their atoms. When elements react, their atoms combine in simple, whole-number ratios. When elements react, their atoms sometimes combine in more than one simple, whole-number ratio
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Exposure of a uranium-bearing crystal to sunlight
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Further testing of this theory had to be put off for a few days because the sky had clouded up and the sun had disappeared. For the next couple of days he left his sample of uranium in a closed drawer along with the photographic plate
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He interpreted this to mean that matter was made up of mostly empty space, but there was a small dense portion of matter that deflected the particles
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Thomson discovered cathode rays and how to calculate ratio of electrical charge to the mass of particles
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Between 1908 and 1917, Robert Millikan measured the charge on an electrons
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As they studied atomic disintegration, they kept seeing that the atomic number (number of protons in the nucleus, equivalent to the positive charge of the atom) was less than the atomic mass (average mass of the atom)