atomic model timeline

  • 200


    How: Continued the work of his mentor, Leucippus Formulated an atomic theory similar to modern science’s understanding of the atom.
    What: His theory suggested that atoms can’t be destroyed and exist in a void. Atoms only differ in shape, position and arrangement.
  • John Dalton

    John Dalton
    What: He pictured atoms as tiny, indestructible, particles, with no internal structure.
    How: Experiments with gases that first became possible at the turn of the nineteenth century led John Dalton in 1803 to propose a modern theory of the atom based on the following assumptions.
  • Joseph John thomson

    Joseph John thomson
    What: He discovers the electron, leading to his "plum-pudding" model.
    How: He used a sealed tube of gas in his experiments when the current wwass on the disks became charged and a glowing beam appeared in the tube.
  • Hantaro Nagaoka

    Hantaro Nagaoka
    How: Nagaoka’s most notable work included the Saturnian model and his work on spectroscopy.
    What: 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.
  • Ernest Rutherford

    Ernest Rutherford
    What: He discovered that uranium emits fast-moving particles that have a have positive charge.
    How: He found out the path of an alpha practicle can be detected by the location of a flash on a screen.
  • Ernest Marsden

    Ernest Marsden
    What: He found out that about one out of every 20,000 atoms were deflected by more than 90 degrees.
    How: He aimed a norrow beam of alpha practicles at the gold. By observing the flash, he could figure out that the path of an alpha practicle after passing through gold.
  • Niels Bohr

    Niels Bohr
    How: He believed an electron in an atom can move from one energy level to another when the atom gains or loses energy.
    Experiment: Electrons move with constant speed in fixed orbits around the nucleus, like the planets around the sun.
  • Luis de Broglie

    Luis de Broglie
    What: He proposes that moving particles like electrons have some praperties of waves. Within a few years, evidence is collected to support this idea.
    How: His hypothesis was soon confirmed in experiments that showed electron beams could be diffracted or bent as they passed through a slit much like light could.
  • Erwin Schrodinger

    Erwin Schrodinger
    What: He develops mathematical equations to describe the motion of electrons in atoms. His work leads to the electron cloud model.
    How: Schrödinger combined the equations for the behavior of waves with the de Broglie equation to generate a mathematical model for the distribution of electrons in an atom.
  • James Chadwick

    James Chadwick
    What: He confirms the existence of neutrons, which have no charge. Atomic nuclei contain neutrons and positively charged protons.
    How: Experiments in Europe caught his eye, especially those of Frederic and Irene Joliot-Curie.
  • Democritus

    What: Democritus suggested that all matter was formed of different types of tiny discrete particles and that the properties of these particles also determined the properties of matter.
    How: This theory had some support from other philosophers, such as Lucretius, but the methods to verify it did not exist in that era, so it was not widely adopted for many centuries.