Atomic Timeline

By jpruyne
  • 430 BCE

    Democritus

    Democritus
    Democritus suggested that everything is made up of small, invisible particles which he called "atomos." He also believed they were different sizes/shapes, were in constant motion in a void, collided, and would bounce off or stick to each other during these collisions.
  • 322 BCE

    Aristotle

    Aristotle
    Did not believe in the atomic theory, but instead that everything was made up of four elements: earth, wind, fire, and air

  • Joseph Proust

    Joseph Proust
    Created the Law of Definite Proportions: A compound is made up of exact proportions of elements regardless of the way the compound was created.

  • Antoine Lavoisier

    Antoine Lavoisier
    Created the Law of Conservation of Matter: Matter is conserved in a chemical reaction, it is neither created nor destroyed.

  • JJ Thomson

    JJ Thomson
    Discovered the electron by experimenting with cathode ray tubes. He also studied the charges in gas, creating a new atomic model which accounted for these charges.

  • Robert Milikan

    Robert Milikan
    Determined the size and charge of an electron and that there was a smallest unit charge.

  • Ernest Rutherford

    Ernest Rutherford
    Concluded that atoms consisted of a small, dense, positively charged nucleus in the center of the atom with negatively charged electrons surrounding it.

  • Niels Bohr

    Niels Bohr
    Created a new model of the atom where the electrons orbited the nucleus, each orbit has a certain level of energy that goes with it, energy is absorbed when it goes from a lower to higher orbit, and is emitted when it goes from a higher to a lower orbit.

  • Schrodiner

    Schrodiner
    Made the quantum mechanical model that predicts the odds of the location of an electron. Electrons were more likely to be found in the dense cloud than in the less dense area outside of the cloud. It also introduced sub-energy levels.

  • Heisnberg

    Heisnberg
    Contributed to quantum mechanics about electron behavior by creating the "uncertainty principle", that states that it is impossible to know exactly where something is and how fast it is going.

  • James Chadwick

    James Chadwick
    Performed an experiment where beryllium atoms were hit with alpha particles. A radiation was produced and Chadwick stated that the radiation was made up of particles with a neutral charge, a neutron.