Atomic Structure Timeline

By denise.kim
  • 470

    Democritus, Greece.

    • "by convention bitter, by convention sweet, but in reality atoms and void"
    • Atoms are known to be eternal, indestructible and unchanging.

  • Newton.

    • Three laws of motion; inertia, action and reaction, and acceleration proportional to force.
    • Gravity within the Solar System is the explanation for tides and a theory of lunar motion.

  • Dalton, London.

    • Atomic Theory; all matter was composed of small indivisible particles called atoms.
    • We now know that atoms cannot be altered of destroyed; they can combine to form more complex structures.

  • G.J. Stony, Ireland.

    • Atomic Theory; all matter was composed of small indivisible particles called atoms.

  • J.J. Thompson, London.

    • English physicist who discovered the electron using a cathode ray tube in 1897.
    • We learn that holds that it is difficult for charged ions to attract each other through insulating water molecules, so they dissociate.

  • Planck, Kiel, Germany.

    • Used the idea of quanta (discrete units of energy) to explain hot glowing matter.
    • Planck's spectrum was obtained by postulating that energy was directly proportional to frequency (E = hv).

  • Nagaoka, Japan.

    • Postulated a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle.
    • Electrons revolve around positively charged particle.

  • Milikan, Morrison, USA.

    • 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.
    • Measurement of the charge on the electron and for his work on the photoelectric effect.

  • E. Rutherford, New Zealand, UK, Canada.

    • 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, Gallopoli, Turkey.

    • Using x-ray tubes, determined the charges on the nuclei of most atoms.
    • This work was used to reorganize the periodic table based upon atomic number instead of atomic mass.

  • Bohr, Copenhagen, Denmark.

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

  • James Chadwick, England.

    • Developed an explanation of atomic structure that underlies regularities of the periodic table of elements.
    • Thus was discovered the neutron.