Atomic Theory

  • John Dalton

    In 1803 the English chemist John Dalton was the first to come up with any evidence that there were such things as atoms, and he was able to show some of their properties. Most scientists accepted his theory as correct, although there were some diehards who maintained that it hadn't actually been proved right up until the beginning of the twentieth century. All of today's historians of science would credit Dalton with the discovery.
  • JJ Thomson

    discovered the electron
  • Nagaoka

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

    Using alpha particles as atomic bullets, probed the atoms in a piece of 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.
  • Moseley

    Using x-ray tubes, 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.
  • Aston

  • 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 sucessive orbital shells of electrons.
  • De Broglie

    Discovered that electrons had a dual nature-similar to both particles and waves. Particle/wave duality. Supported Einstein.
  • De Brogile

  • Heinsenburg

    Described atoms by means of formula connected to the frequencies of spectral lines. Proposed Principle of Indeterminancy - you can not know both the position and velocity of a particle.
  • Walton

  • Walton

  • Schrodinger

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

  • Anderson

    discovered the anti-electron
  • Chadwick

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

    Conducted the first controlled chain reaction releasing energy from the atoms nucleus.
  • Segre/Chamberlain

    detected the anti-proton