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Democritus thought about what happens when you cut the smallest matter into a smaller piece, in about 450 B.C.
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Isaac Newton theorized a mechanical universe with small, solid masses in motion.
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Around 1800, a British chemist named John Dalton revived Democritus’s early ideas about the atom.
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Dmitri Mendeleev created the periodic table.
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Wilhelm Roentgen discovered x-rays.
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Thomson discovered electrons.
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The first ray tube was invented by William Crookes in 1897. The development of the television was based on the CRT.
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Rutherford discovered the nucleus.
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Max Planck proposed the idea of quantization to explain how a hot, glowing object emitted light.
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Robert A Millikan created a way to measure the electric charge of a single electron, using the oil drop experiment.
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In 1911, Rutherford used alpha particles to study atoms. He aimed a beam of alpha particles at a very thin sheet of gold foil.
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In 1913, Niels Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. Electrons should move around the nucleus but only in prescribed orbits.
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Francis William Aston used a mass spectrograph to identify 212 isotopes.
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Erwin Schrödinger developed the probability function for the Hydrogen atom. The cloud model represents a sort of history of where the electron has probably been and where it is likely to be going.
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Enrico Fermi created the first man-made nuclear reactor.