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Democritus made the theory that all matter is made up of small, indestructible units he called "atoms".
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John Dalton proposed elements were made of atoms that were identical and had the same mass and that compounds were atoms from different elements combined together.
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Julius Plucker built one of the first cathode-ray tubes.
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Dmitri Mendeleev created the first periodic table based on atomic masses.
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G.J Stoney theorized that electricity was comprised of negative particles called electrons.
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Wilhelm Roëntgen discovered x-rays.
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Ernest Rutherford discovered alpha, beta, and gamma rays in radiation.
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Marie Sklodowska Curie discovered radium and polonium and coined the term radioactivity after studying the decay process of uranium and thorium.
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Fredrick Soddy came up with the term "isotope" to explain the unintentional breakdown of radioactive elements.
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Hantaro Nagaoka proposed an atomic model called the Saturian Model to describe the structure of an atom.
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H.G.J Moseley discovered that the number of protons in an element determines its atomic number and created a modern periodic table.
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Niels Bohr proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit.
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Lise Meitner, Hahn, and Strassman discovered nuclear fission.
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James Chadwick discovered neutrons, particles whose mass was close to that of a proton.