Atomic theory timeline

By bec5902
  • 320

    Democritus

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

  • Isaac Newton

    Proposed a mechanical universe with small solid masses in motion.

  • John Dalton

    Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass.

  • J. Plucker

    Built one of the first gas discharge tubes ("cathode ray tube").

  • Sir William Crookes

    Discovered cathode rays had the following properties: travel in straight lines from the cathode; cause glass to fluoresce; impart a negative charge to objects they strike; are deflected by electric fields and magnets to suggest a negative charge; cause pinwheels in their path to spin indicating they have mass.

  • J.J. Thomson

    Used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 10 8 coulombs/gram.

  • Rutherford

    Studied radiations emitted from uranium and thorium and named them alpha and beta.

  • Nagaoka

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

  • Albert Einstein

    Published the famous equation E=mc 2

  • Ernest Rutherford

    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.

  • Aston

    Discovered the existence of isotopes through the use of a mass spectrograph.

  • Cockcroft/Walton

    Built an early linear accelerator and bombarded lithium with protons to produce alpha particles

  • Schrodinger

    Viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom.

  • Paul Dirac

    Proposed anti-particles . Anderson discovered the anti-electron (positron) in 1932 and Segre/Chamberlain detected the anti-proton in 1955..

  • James Chadwick

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

  • Lise Meitner, Hahn , Strassman

    Conducted experiments verifying that heavy elements capture neutrons and form unstable products which undergo fission. This process ejects more neutrons continuing the fission chain reaction.

  • Glenn Seaborg

    Synthesized 6 transuranium elements and suggested a change in the layout of the periodic table.

  • Enrico Fermi

    Conducted the first controlled chain reaction releasing energy from the atoms nucleus.