Atomic Theory Timeline

  • Robert Boyle

    Helped develop the definition of an element, also with the "death" of the four elements- Earth, Fire, Air, Water.
  • Antoine Lavoisier

    Disocovered that water was made of Hydrogen and Oxygen. Also invented the analytical balanance and showed that chemical elements were neither created nor destroyed- Conservation of Mass
  • Carl Scheele

    Discovered Oxygen and identified Molybdenum, Tungsten, Barium, Hydrogen, Chlorine.
  • Joseph Priestley

    Published Oxygen findings before Carl Scheele.
  • Joseph Proust

    Created Law of Definite Proportions and studied Copper Carbonate, 2 Tin Oxide, 2 Iron Sulfide.
  • John Dalton

    Created Modern Atomic Theory.
  • Julius Plucker

    Built the first Cathode Ray Tube.
  • William Crookes

    Discovered Cathode Ray's properties.
  • Jean Baptiste Perrin

    Confirmed Einstein's ideas on Browmian motion by calcuating Avogadro's Constant, proving Dalton's Atomic Theory.
  • J.J. Thompson

    Studied "canal rays" and found they were associated with the proton H+. Used a CRT to experimentally determine the charge to mass ratio of an electron.
  • Marie and Pierre Curie

    Studied Uranium and Thorium and called their spontaneous decay process "radioactivity". Also discovered radioactive elements Polonium and Radium.
  • Ernest Rutherford

    Studied radiations emitted from Uranium and Thorium and named them Alpha and Beta.
  • Frederick Soddy

    Observed spontaneous disintegration of radioactive elements into variants he called "isotopes" or totally new elements. Discovered "half life", made initial calculations on energy released during decay.
  • Hans Geiger

    Developed an electrical device to "click" when hit with Alpha particles.
  • Robert Millikan

    Measured the charge of an electron with his oil-drop apparatus. He proved Thomson's hypothesis that the mass of an electron is at least 1000 times smaller than the smallest atom.
  • Ernest Marsden

    Discovered structure of an atom with the "gold foi" experiment.
  • James Chadwick

    Using alpha particles discovered a neutral atomic particle with a mass of a proton- Neutron.