History of the Atom

Timeline created by ellencwade
  • Newton writes about forces of attraction

    Newton writes about forces of attraction
    Sir Isaac Newton writes about the possible existence of unseen electrical forces of attraction that hold matter together.
  • Modern Definition of "Element" is Accepted

    Modern Definition of "Element" is Accepted
    Most scientists at this time accepted the modern defiinition of an element: a substance that cannot be broken down into any simpler substances.
  • Dalton's Atomic Theory

    Dalton's Atomic Theory
    John Dalton explains the law of conservation of mass, the law of definite proportions, and the law of multiple proportions in his Atomic Theory.
  • First Periodic Table of Elements

    First Periodic Table of Elements
    Dmitri Mendeleev aranged 7 elements into groups according to atomic mass and chemical properties.
  • J.J. Thomson experiments with cathode rays

    J.J. Thomson experiments with cathode rays
    Later, Thomson's experiments are replicated, leading to the discovery of subatomic particles.
  • Discovery of the Electron

    Discovery of the Electron
    Robert Millikan discovers the electron
  • Discovery of the Nucleus

    Discovery of the Nucleus
    Ernest Rutherford, Hans Geiger, and Ernest Marsden discover the nucleus. During an experiment, Rutherford aimed alpha particles at a thin gold foil, expecting them to pass through the foil. Most of the particles did, but a small quantity "bounced back," suggesting that the particles bounced off of something in the gold foil.
  • Bohr Model Proposed

    Bohr Model Proposed
    Niels Bohr proposed a model often compared to the solar system. He believed that electrons orbited the nucleus like the planets orbit the sun.
  • Proton is named

    Proton is named
    Ernest Rutherford names the positively charged particle of an atom the "proton"
  • Idea of the neutron is proposed

    Idea of the neutron is proposed
    Idea of the neutron is proposed by Ernest Rutherford
  • Chadwick proves the existence of neutrons

    Chadwick proves the existence of neutrons
    James Chadwick proves that neutral particles in atoms, neutrons, exist.