History of Atomic Theory

By hamika
  • 470

    (B.C) Democritus, Greece.

    "by convention bitter, by convention sweet, but in reality atoms and void"
  • Newton, England

    Projected a mechanical universe with small solid masses in motion.
  • Dalton, England

    Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass.
  • George Johnstone Stoney (Ireland)

    Claimed atoms could eject small negatively charged particles, which he named as electrons. Also proposed electricity was made of electrons.
  • JJ Thomson, England

    Experimented on a Cathode Ray Tube to determine the charge to mass ratio (e/m) of an electron =1.759 x 10 8 coulombs/gra
  • Planck, Germany

    Used the idea of quanta (discrete units of energy) to explain hot glowing matter.
  • Nagoaka, Japan

    ostulated a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle.
  • Millikan, America

    Oil drop experiment 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, New Zealand

    Using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm) gold foil . He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus.
  • H.G.J. Mosely, England

    Using x-ray tubes, determined the charges on the nuclei of most atoms. He wrote "The atomic number of an element is equal to the number of protons in the nucleus". This work was used to reorganize the periodic table based upon atomic number instead of atomic mass.
  • Bohr, Denmark

    Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of successive orbital shells of electrons
  • James Chadwick, England

    Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron.