Atomic Theory

By Chelsea.Bryant
  • 460

    Democritus

    Democritus
    (460-370BC)
    First proposed the existence of an ultimate particle.

  • Issac Newton

    Issac Newton
    (1704)
    Newton formulated a theory of light, the three laws of motion and suggested a mechanical universe with small, solid masses. Newton suggested that atoms are held together with attractions, otherwise known as forces. He also stated that "matter is formed of solid, massy impenetrable particles”.

  • John Dalton

    John Dalton
    (1776-1844)
    John proposed the Law of Multiple Proportions.
    He also developed the concept of the mole and proposed a system of symbols to represent atoms of different elements.

  • J.J. Thomson

    J.J. Thomson
    (1856-1940)
    J.J. discovered the electron in 1897 using the cathrode ray tube.
    He also studied proton and came up with the Plum Pudding model.

  • Dmitri Mendeleev

    Dmitri Mendeleev
    (1869)
    He arranged elements by atomic mass and similar properties.

  • Ernest Rutherford

    Ernest Rutherford
    (1871-1937)
    Ernest used the gold foil method to propose the nuclear atom in 1911. In 1920 he theorized the neutron.

  • H.G. Moseley

    H.G. Moseley
    (1887-1915)
    Modern Pt, arranged by atomic number?

  • James Chadwick

    James Chadwick
    (1891-1974)
    James proved the existance of the neutron in 1932.

  • Marie Curie

    Marie Curie
    (1898)
    Marie did research on radioactivity. she discovered polonuim in 1898, isolating radioavtive isotopes.

  • R.A. Millikan

    R.A. Millikan
    (1908)
    R.A. measuring charge on the election and photoelectric effect.

  • Hans Geiger

    Hans Geiger
    (1909)
    Geiger-marsden experiement discovered atomic nucleus.

  • Niels Bohr

    Niels Bohr
    (1922)
    Fundamental contributions to the understanding of atomic structure and quantum mechanics.
    By expanding on Rutherford’s earlier theory Bohr published his theory which suggested that electrons travel in specific orbits around the nucleus, that outer orbits can hold more electrons than the inner orbits and that these orbits determine the chemical properties of the atom.

  • Lise Meitner

    Lise Meitner
    Jan 13, 1939
    Lise was part of a team that discovered nuclear fission.