Timeline of Atomic Theory

Timeline created by wendyyy
  • 460


    Date: 460-370 BC
    Location: Greece
    Idea/experiment: Continued the work of his mentor, Leucippus. He formulated an atomic theory similar to modern science’s understanding of the atom.
    Contibution to the understanding of the atom: His theory suggested that atoms can’t be destroyed and exist in a void. Atoms only differ in shape, position and arrangement
  • Isaac Newton

    Isaac Newton
    Date: 1704
    Location: England
    Idea/experiment: Newton formulated a theory of light, the three laws of motion and suggested a mechanical universe with small, solid masses in motion.
    Contribution to our understanding of the atom: 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
    Date: 1803
    Location: England
    Idea/experiment: He proposed an atomic theory.
    Contribution to our understanding of the atom: Dalton stated (1) all matter was composed of small indivisible particles termed atoms, (2) atoms of a given element possess unique characteristics and weight, and (3) three types of atoms exist: simple (elements), compound (simple molecules), and complex (complex molecules).
  • George Johnstone Stoney

    George Johnstone Stoney
    Date: 1894
    Location: Ireland
    Idea/experiment: Introduced the term electron and estimated the charge carried by a single hydrogen atom.
    How this contributed to our understanding of the atom: Stoney introduced the term electron as the “fundamental unit quantity of electricity”.
  • Joseph John Thomson

    Joseph John Thomson
    Date: 1897
    Location: England
    Idea/experiment: The discovery of the electron and of isotopes, and the invention of the mass spectrometer.
    Contibution to our understanding of the atom: With the Nernst-Thomson rule he explains that it is difficult for charged ions to attract each other through insulating water molecules, so they dissociate.
  • Max Planck

    Max Planck
    Date: 1900
    Location: Germany
    Idea/experiment: A scientific philosopher Planck's Principle was that "A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die and a new generation grows up that is familiar with it."
    Contribution to our understanding of the atom: Planck, a German physicist, is considered the founder of the quantum theory.
  • Hantaro Nagaoka

    Hantaro Nagaoka
    Date: 1903
    Location: Japan
    Idea/experiment: Nagaoka’s most notable work included the Saturnian model and his work on spectroscopy
    Contribution to our understanding of the atom: Nagaoka created an early, incorrect model of an atom using an analogy based on Saturn’s rings. He also worked with British physicist C. G. Knott on spectroscopy.
  • Robert Andrews Millikan

    Robert Andrews Millikan
    Date: 1909
    Location: America
    Idea/experiment: Millikan is famous for his measurement of the charge of an electron and his work on the photoelectric effect.
    Contribution to our understanding of the atom: Using an oil drop experiment Millikan measured the charge of an electron.
  • Ernest Rutherford

    Ernest Rutherford
    Date: 1911
    Location: Britain/ New Zealand
    Idea/experiment: Rutherford was a chemist and a physicist who was also known as the father of nuclear physics
    Contribution to our understanding of the atom: Rutherford discovered the concept of the radioactive half life. He also differentiated and named alpha and beta radiation. Rutherford is credited for performing the first splitting of an atom.
  • Henry Gwyn-Jeffreys Moseley

    Henry Gwyn-Jeffreys Moseley
    Date: 1914
    Location: England
    Idea/experiment: Studying under Rutherford, Moseley developed the application of X-ray spectra to study atomic structure.
    Contibution to our understanding of the atom: By measuring the wavelengths of the x-rays given off by certain metals, Moseley was able to determine the number of positive charges in the nucleus of an atom. This was the first concept of the atomic number.
  • Neils Bohr

    Neils Bohr
    Date: 1922
    Location: Denmark
    Idea/experiment: Fundamental contributions to the understanding of atomic structure and quantum mechanics.
    Contribution to our understanding of the atom: 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.
  • James Chadwick

    James Chadwick
    Date: 1932
    Location: England
    Idea/experiment: Famous for his discovery of the neutron.
    Contriution to our understanding of the atom: Chadwick discovered the neutron, named because of the lack of electric charge, which was previously an unknown particle in the nucleus of an atom.