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Democritus hypothesized that atoms cannot be destroyed, differ in size, shape and temperature, are always moving, and are invisible.
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His theory said all matter is made of atoms, atoms are indivisible and indestructible, all atoms of a given element are identical in mass and properties, compounds are formed by a combination of two or more different kinds of atoms, and a chemical reaction is a rearrangement of atoms.
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He discovered the electron.
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Measured the charge of the electron using an oil drop experiment.
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He discovered the nucleus.
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He discovered the atomic nucleus.
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He discovered the neutron.
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