Scientists Contributing to Atomic Theorey

By LA Pie
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    Democritus

    Democritus
    Democritus had the idea that if you kept cutting an object, you would eventually end with an uncuttable piece which he named an atom. He also believed that everything was made up of small atoms moving in a void.
  • John Dalton

    John Dalton
    Dalton believed that all matter is composed of atoms, which are small particles that cannot be created, divided, or destroyed. He also proved that atoms with the same element are identical and different elements have unlike types of atoms. Also, he explained how atoms join together to make new substances.
  • George Johnstone Stoney

    George Johnstone Stoney
    Stoney proposed that electricity was made of negatively charged particles in atoms called electrons.
  • Joseph John Thomson

    Joseph John Thomson
    Thomson showed a mistake in Dalton's theory. There were actually smaller particles in atoms! Thomson conducted the Cathode-Ray Tube experiment and discovered that the smaller particles in atoms were negatively charged. He had discovered electrons. This also led him to believe that there were positive and negative forces in the atom.
  • Max Planck

    Max Planck
    Planck developed the quantum theory by studying radiation. He also hypothesized that matter was discrete, not continuous.
  • Plum-Pudding Model

    Plum-Pudding Model
    Thomson presented his model of the atom (also known as the Chocolate Chip Ice-Cream model). It had electrons throughtout it.
  • Ernest Rutherford

    Ernest Rutherford
    Rutherford tested Thomson's theory by conducting the Gold Foil Experiment. He discovered that atoms are mostly empty space with a dense, positive nucleus. He learned that a particle headed straight for the nucleus would be pushed back in the same direction it came, because like charges repel. HIs model of the atom shows that the center of the atom is the nucleus and has electrons surrounding it.
  • Henry Moseley

    Henry Moseley
    Moseley was the first to justify the atomic number, which gives the number of protons in a nucleus, by studying the X-ray spectra of each element. His work was even used to rearrange the periodic table based upon atomic number instead of atomic mass!
  • James Chadwick

    James Chadwick
    Chadwick contributed to the atomic theory by proving the existence of uncharged particles in atoms, neutrons. He discovered that neutrons help reduce the repulsion between protons and stabilize the atom's nucleus. His discovery also played a key role in nuclear fission. His atomic model shows protons and neutrons in the nucleus with electrons outside.
  • Niels Bohr

    Niels Bohr
    Bohr, a Danish scientist who worked with Rutherford, studied how atoms reacted to light. He proposed that electrons are located in levels at the certain distances from the nucleus.In his Planetary Model in 1913 the nucles is surrounded by electrons at different energy levels. There are no paths beteen the levels in his model. The electrons can jump form one path to another.
  • Robert Millikan

    Robert Millikan
    Millikan determined the charge and mass of an elcetron by conducting the Oil Drop Experiment. He proved Thomson's theory that the mass of an electron is at least 1000 times smaller than the smallest atom.