History of Atoms

  • 470


    Developed a theory that Matter was composed of tiny particles called atoms, that could bond with other atoms to create more.
  • Period: 470 to

    Development of Atomic Theory

  • Newtown

    Proposed a mechanical universe with small solid masses in motion.
  • Dalton

    Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass.
  • G. J. Stoney

    Discovered that electricity was made up of negative particles called ‘electrons’.
  • J. J. Thomson

    The ‘Plum Pudding Theory’.
  • Planck

    Used the idea of quanta which is discrete units of energy, to explain hot glowing matter.
    Created Planck’s constant and Planck’s Law of Black-body Radiation.
  • Nagaoka

    Created a ‘Saturnian’ or Planetary model of the atom, with flat rings representing electrons, revolving around a positively charged particle, the model representing electrons revolving around a nucleus which was bound by electrostatic forces.
  • Millikan

    Conducted the ‘Millikan Oil drop experiment ‘ which determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron.
  • E. Rutherford

    Established that the nucleus was very dense, very small and positively charged. Also assumed that the electrons were located outside the nucleus.
  • H.G.J. Moseley

    Discovered each nucleus had an ‘atomic number’ that was equal to the number of positive charges (protons) associated.
  • Bohr

    Developed the ‘Shell model’ that had atoms built up of successive orbital shells of electrons.
  • James Chadwick

    Used alpha particles leading to the discovery of a neutral atomic particle with a mass close to a proton. Thus, the neutron was discovered.