Atomic Theory Timeline

  • 4000 BCE


    Alchemy was the belief that all things are built from one of the four elements, earth, water, wind, and fire. The idea that all things are made of said elements caused chemists to try to mix various metals, specifically lead, in an attempt to make gold.
  • 700 BCE

    Asharya Kanada

    Asharya Kanada
    Kanada theorized that atoms existed as an indestructible particle of matter, in addition, these particles could be combined to create reactions such as fruit ripening.
  • 450 BCE

    Ancient Greece

    Ancient Greece
    The idea of the atom was created in ancient Greece based on the theory that after cutting rock in half so many times one will eventually have a rock so small it is indivisible, or in ancient Greek, "atomos". They presented the idea that all matter was made of small "atomos" in many shapes and sizes that were constantly moving and colliding.
  • John Dalton

    John Dalton
    John Dalton created the first set of rules that all atoms follow, they are:
    1. All matter is made of atoms
    2. atoms of the same element have the same property
    3. compounds are made by combining 2 or more atoms
    4. A chemical reaction is the rearrangement of atoms
  • J.J. Thompson

    J.J. Thompson
    J.J. Thompson introduced the idea of charged particles within an atom, his model showed a clump of positive and negative charges much like a "Plum Pudding" giving it its name as a plum pudding model. Even though his model was wrong the introduction of charges inside of atoms is still used today.
  • Max Planck

    Max Planck
    Max Planck derived a constant that is able to show the amount of radiation being emitted from a black body is proportional to the amount being absorbed.
  • Marie Sklodowska Curie

    Marie Sklodowska Curie
    Marie Curie discovered, through experiment, that an element will radiate a constant amount since radiation is only effected by the element's atomic structure as opposed to physical reactions or conditions.
  • Ernest Rutherford

    Ernest Rutherford
    Rutherford expended on J.J. Thompson's atomic model but instead of believing all charges are dispersed inside the atom he believed that there was a positive nucleus surrounded by a cloud of negatively charged particles, a planetary model.
  • Hantaro Nagaoka

    Hantaro Nagaoka
    Nagaoka expanded on the planetary atomic model by determining that the atom was like Saturn as the nucleus is significantly larger than the electrons surrounding it.
  • Niels Bohr

    Niels Bohr
    Niels Bohr expended on Rutherford's atomic model and said that opposed to a cloud of electrons surrounding the positive nucleus there is an orbit of electrons with different levels.
  • Louis de Broglie

    Louis de Broglie
    De Broglie's contribution to the atomic theory was that electrons act as waves do as opposed to particles like protons and neutrons.
  • Werner Heisenberg

    Werner Heisenberg
    Heisenberg added to Schrodinger's contribution with his uncertainty principle. The uncertainty principle states that there is no way to be sure a particle will be at any given point at any given time.
  • Wolfgang Pauli

    Wolfgang Pauli
    Pauli stated that no two electrons could be in the same quantum space at the same time and could not have the same quantum numbers. This allows for the orbital to be possible.
  • Erwin Schrodinger

    Erwin Schrodinger
    Schrodinger Found a mathematical way to determine the likeliness that an electron will be at any given spot at any given time.
  • James Chadwick

    James Chadwick
    James Chadwick discovered that in a nucleus, in addition to the proton, there is a neutral particle called a neutron. This was found to support the fact that electrons are essentially weightless yet the weight of atoms assuming there is no neutron would say otherwise.
  • Irene Joliot-Curie

    Irene Joliot-Curie
    Discovered that radioactive elements can be created by tampering with (removing or adding particle) atoms to create radioactive forms of those atoms. this contribution had a big impact on the study of radioisotopes.
  • Satyendra Nath Bose

    Satyendra Nath Bose
    After discovering the boson, Bose, and Einstein discovered the Bose-Einstein condensate, a collection of bosons with integer spin.
  • Albert Einstein

    Albert Einstein
    Einstein found a way to observe and calculate the amount of power that is produced by the particles within the atom by helping with the atomic bomb and E=mc^2.
  • Rosalind Franklin

    Rosalind Franklin
    Franklin was an x-ray crystallographer who dedicated her life to the study of coal and carbon. her studies were used in creating stronger carbon fibers as well as controlling nuclear reactions.
  • Ronald J. Gillespie

    Ronald J. Gillespie
    Gillespie worked to extend the valence shell electron pair repulsion theory which can be used to predict molecule shapes based on electron pairs within the valence shell.
  • Richard F.W. Bader

    Richard F.W. Bader
    Bader Discovered that an electrons density is a major part of the explanation for the way they act and why the move how they do.