Atomic Theory Timeline

  • 100


    Democritus claimed that everything is made up of atoms. These atoms are physically indivisible; between atoms lies empty space; atoms are indestructible; have always been, and always will be, in motion; there are an infinite number of atoms and kinds of atoms, which differ in shape, and size and the real time this happened is between 460 BCE to 370 BCE.
  • 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.
  • James Clerk Maxwell

    Proposed electric and magnetic fields filled the void.
  • G.J. Stoney

    Proposed that electricity was made of discrete negative particles he called electrons
  • Nagaoka

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

    He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus.
  • H.G.J. Moseley

    He said"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

    His atomic model had atoms built up of sucessive orbital shells of electrons.
  • Schrodinger

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

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