Atomic theory1

History of The Atomic Theory

  • 400 BCE

    Democritus

    Democritus was the first to introduce the Atomic Theory stating that all matter is made up of small indestructible units called atoms.
  • Period: 400 BCE to

    Atom Theory

    Timeline
  • Isaac Newton

    Isaac Newton theorized theorized a mechanical universe with small, solid masses in motion.
    The first law states that every object in the state of uniform motion tends to remain in the same state of motion unless an external force is applied to it
    The second law states that the net force of an object is proportional to the time rate of change to its linear momentum.
    The third law states that for every action there is an equal and opposite reaction.
  • John Dalton

    Proposed that elements consisted of atoms that were identical and had the same mass and that compounds were atoms from different elements combined together.
  • Michael Faraday

    Michael Faraday developed the two laws of electrochemistry.
    m=(Q/F)*(M/z)
    m is the mass of the substance liberated at an electrode in gms
    Q is the total electric charge passed through the substance in coulombs
    F = 96500 C mol−1 is the Faraday constant
    M is the molar mass of the substance in grams per mol
    z is the valence number of ions of the substance
    n=(It/F)*(1/z)
    n is the amount of substance ("number of moles") liberated: n = m/M
    t is the total time the constant current was applied.
  • J. Plucker

     J. Plucker built one of the first cathode-ray tubes.
  • Dmitri Meneleev

     Dmitri Mendeleev created the periodic table. He formulated the Periodic Law, created a farsighted version of the periodic table of elements, and used it to correct the properties of some already discovered elements and also to predict the properties of eight elements yet to be discovered. He arranged the periodic table in order from smallest to largest mass size.
  • James Clerk Maxwell

     James Clerk Maxwell proposed the theory of electromagnetism and made the connection between light and electromagnetic waves.
  • G.J. Stoney

     G.J. Stoney theorized that electricity was comprised of negative particles he called electrons
  • E. Goldstein

    E. Goldstein discovered canal rays, which have a positive charge equal to an electron.
  •  Wilhelm Roentgen

     Wilhelm Roentgen discovered x-rays
  • J.J. Thomson

    J.J. Thomson discovered the electron by experimenting with a Crookes, or cathode ray, tube. He demonstrated that cathode rays were negatively charged.
  • Ernest Rutherford

    Rutherford discovered alpha, beta, and gamma rays in radiation in his gold foil experiment in which he demonstrated that the atom has a tiny and heavy nucleus.
  • Maie Sklodowska Curie

    Marie Sklodowska Curie discovered radium and polonium and coined the term radioactivity after studying the decay process of uranium and thorium
  • Max Planck

     Max Planck proposed the idea of quantization to explain how a hot, glowing object emitted light.
  • Frederick Soddy

    Frederick Soddy came up with the term "isotope" to explain the unintentional breakdown of radioactive elements.
  • Hantaro Nagaoka

    Hantaro Nagaoka proposed an atomic model called the Saturnian Model to describe the structure of an atom.
  • Richard Abegg

    Richard Abegg found that inert gases have a “stable electron configuration.”
  • Hans Geiger

    Hans Geiger invented a device that could detect alpha particles.
  • H.G.J. Moseley

    H.G.J. Moseley discovered that the number of protons in an element determines its atomic number
  • Francis William Aston

    Francis William Aston used a mass spectrograph to identify 212 isotopes
  • Niels Bohr

    Niels Bohr proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit.
  •  Louis de Broglie

     Louis de Broglie proposed that electrons have a wave/particle duality
  • Cockcroft and Walton

     Cockcroft / Walton created the first nuclear reaction, producing alpha particles
  • Paul Dirac

    Paul Dirac proposed the existence of anti-particles
  •  James Chadwick

    James Chadwick bombarded beryllium atoms with alpha particles. An unknown radiation was produced. James Chadwick discovered neutrons, particles whose mass was close to that of a proton.
  •  Lise Meitner

     Lise Meitner Hahn Strassman discovered nuclear fission
  • Glenn Seaborg

    Glenn Seaborg discovered eight trans-uranium elements
  • Enrico Fermi

    Enrico Fermi created the first man-made nuclear reactor