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Democritus' atomic theory stated that all matter is made up of small, indestructible units he called atoms atoms.

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Elements, according to John Dalton, are made up of identical atoms of the same mass, and compounds are atoms from different elements combined together.

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The periodic table was invented by Dmitri Mendeleev.

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Thomson calculated the charge-to-mass ratio of electrons.

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In radiation, Rutherford discovered alpha, beta, and gamma rays.

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After studying the decay of uranium and thorium, Marie Sklodowska Curie discovered radium and polonium and coined the term radioactivity.

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The word "isotope" was created by Frederick Soddy to describe the unintentional breakdown of radioactive elements.

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Hans Geiger invented a device that could detect alpha particles.

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According to Niels Bohr's atomic structure theory, an atom's outer orbit could hold more electrons than its inner orbit.

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James Chadwick discovered neutrons, particles with a mass close to that of a proton.

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The three of them discovered nuclear fission.

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Glenn Seaborg was the discoverer of eight transuranium elements.

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Enrico Fermi was the first to build a man-made nuclear reactor.