Timeline- Atomic Structure

  • Jun 29, 1450


    (450 B.C) Created 1st atomic theory: proposed that all matter is made up of particles called atoms, meaning indivisible.
  • Issac Newton

    Issac Newton
    Used small solid masses in motion to propose a mechanical universe
  • John Dalton

    John Dalton
    Created 1st useful Atomic theory: Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass.
  • G. J. Stoney

    G. J. Stoney
    Proposed that electricity was made of discrete negative particles he called electrons
  • J. J. Thomson

    J. J. Thomson
    Discovered the first electron. Determined the charge to mass ratio (e/m) of an electron =1.759 x 10 8 coulombs/gram.
    found ‘canal rays’ were associated with the proton H + .
  • Max Planck

    Max Planck
    Inventor of Quantum theory: explained hot glowing matter.
  • Nagaoka

    Postulated a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle.
  • R. A. Millikan

    R. A. Millikan
    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.
  • Sir Ernest Rutherford

    Sir Ernest Rutherford
    Father of nuclear physics: discovered that the atom's nucleus is very small in relation to the entire atom. He proposed that the negatively charged electrons were revolving around a heavier, charged nucleus.
  • H. G. J. Mosely

    H. G. J. Mosely
    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.
  • Niels Bohr

    Niels Bohr
    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

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