Timeline of Atomic theory

  • 350


    Aristotle disagreed with Democritus’s theory about atoms and believed the world was created from three basic elements fire, earth, air and water
  • 400


    Democritus created the first model of an atom a model of the atom. He was the first one to discover that all matter is made up of invisible particles called atoms. He also discovered that atoms are solid, insdestructable, and unique. HIs model was just a round solid ball. Democritus didn't know about a nucleus or electrons, all he knew was that everything is made of atoms.
  • John Dalton

    John Dalton created the Atomic Theory of Matter, a composition of previous findings by Democritus and his own findings. He included in this theory that all matter is made of atoms, that atoms cannot be created nor destroyed and also, atoms of different elements combine in whole ratios to form chemical compunds.
  • J.J. Thomson

    J.J. Thomson discovered the electron, which led him to create the "plum pudding" atomic model. In this model, he thought that the atom was mostly positive, and negative electrons wandered around the atom. The "plum pudding" model influenced other scientists improve upon this model
  • Robert Millikan

    Robert Millikan further developed upon J.J. Thomson's finding of the electron. J.J. Thomson predicted that the electron was 1000 time smaller than the atom. Millikan wanted to prove this hypothesis. He preformed an "oil-drop experiment" in which he found that J.J. Thomson theory about the electron correct.
  • Ernest Rutherford

    Ernest Rutherford thought that J.J. Thomson's model was incorrect, so he created his own one He created the nucleus, and proposed that instead of the positive matter being the whole atom, it was just in the middle. He said the atom was mostly empty space and that the electrons surrounded the positive nucleus. T
  • Niels Bohr

    Niels Bohr decided to make a new model based off of Rutherford's model, but changed the orbit of the electron. Also, he created energy levels in the atom, where only a certain amount of electrons could fit on one energy level of the atom.
  • Erwin Schrodinger

    Erwin Scrhodinger disagreed with Bohr's theory, so he created his own. He proposed that the only way to find the location and energy of an electron in an atom was to calculate its probability of being a certain distance from the nucleus.
  • Werner Heisenberg

    Werner Heisenberg proposed that you can't know the exact velocity and momentum of the electron at the same time, which means you can't know the exact location of the electron. This proved an error in Bohr's model because of the uncertainty of the location of an electron’s
  • James Chadwick

    Jame Chadwick discovered the neutron. Prior to this discovery, Rutherford had found that the nucleus was made of positive matter. Chadwick knew that the atom was neutral becayse the posttive and negitive charges cancelled each other out. but there was still a problem with the mass not adding up in the atom, this lead to Chadwick finding the nutreal part of the atom, the neutron.