Atomic Theory Timeline

  • Democritus 460 BC- 370 BC

    The atoms in Democritus theory themselves remain unchanged, but move about in space to combine in various ways to form all macroscopic objects.
  • John Dalton

    John Dalton
    John Dalton's theory stated that elements consisted of tiny particles called atoms. He said the reason an element is pure is because atoms in elements are identical and have the same mass. He also said that the reason elements differed from each other was because the mass was different.
  • J.J. Thomson

    J.J. Thomson
    J.J. Thomson discovered the electron by using a Cathode Ray and vacuum tube.
  • Earnest Rutherford

    Earnest Rutherford
    Rutherford, Hans Geiger and Ernest Marsden did the Geiger-Marsden experiment, an attempt to examine the structure of the atom. It showed the existence of the nucleus and was a big part of the Rutherford model of the atom. He won the Nobel prize in 1908.
  • Robert Millikan

    He measured the electrical charge of an electron by spraying minute drops of oil into a specially built chamber. It was called the Oil-drop experiment.
  • Niels Bohr

    Niels Bohr
    This model was proposed by Niels Bohr in 1915. Protrons and neutrons were at the Center of the atom (nucleus). Electrons are orbiting the nucleus. The Bohr model was not completely correct.
  • Electron cloud

    Electron cloud
    The electron cloud model was created after Niel Bohrs' model in 1913. It was created throughout the 20th century. It consists of electrons orbiting the nucleus.
  • James Chadwick

    James Chadwick proofs the existence of the neutron in 1932 and wins a Nobel Prize in 1935. He determined that neutrons existed and that their mass is 0.1% more that the proton's.
  • Erwin Schrödinger

    He contributed to the wave theory of matter, a form of quantum physics, and he devised the mathematical equation of wave mechanics.