Atom History

By cathiee
  • 370

    Democritus

    Democritus
    Matter is made of small indivisible particles which have different form, position and arrangements. Democritus named these particles atoms.

  • John Dalton

    John Dalton
    Developed an atomic theory stating that spherical atoms had measureable properties of mass. Pictures atoms as tiny, indestructible particles, with no internal structure.

  • John Dalton Atomic Model

    John Dalton Atomic Model
    Tiny, Solid Sphere

  • Goldstein

    Goldstein
    Observed a cathode-ray tube and found rays traveling in the direction opposite to that of the cathode rays. He called these rays canal rays and concluded that they were composed of positive particles.

  • J.J Thomson

    J.J Thomson
    Discovers the electron and used cathode ray tubes to determine the charge to mass ration of an electron to be 1.759 x 10^8 Coulombs/gram. Found canal rays were associate with a proton, H+. He pictures electron embedded in a sphere of positive electrical charge.

  • J.J Thomson

    J.J Thomson
    • Sphere with posotive charge throughout
    • Negatively charged particle (electron)

  • Ernest Rutherford

    Ernest Rutherford
    Discovers alpha and beta rays emitting from radium. First artifically induced nuclear reaction. Used nitrogen and alpha particles to obtain an oxygen isotope and protons. Finds that an atom has a small, dense, positively charged nucleus. Electrons move around the nucleus.

  • Ernest Rutherford Atomic Model

    Ernest Rutherford Atomic Model
    Orbits = path of a moving electron

  • Neils Bohr

    Neils Bohr
    Publishes papaer regarding combining nuclear and quantum theories. The electron moves in a circular orbit at fixed distances from the nucleus.

  • Neils Bohr's Atomic Model

    Neils Bohr's Atomic Model
    An electron can gain or lose energy by changing its orbit.

  • Robert Millikan

    Robert Millikan
    The U.S physicist carried out experiments to find the quantity of charge carried by an electron. Calculated the mass of the electron.

  • Erwin Schrodinger

    Erwin Schrodinger
    Saw electrons as a continuous cloud and developed wave mechanics to be a mathematical model for the atom.

  • Erwin Schrodinger's Atomic Model

    Erwin Schrodinger's Atomic Model
    • The electron cloud is a visiial model of the probable locations of electrons in an atom. The probability of finding an electron is higher in the denser regions of the cloud.
    • The nucleus contains protons and neutrons.

  • James Chadwick

    James Chadwick
    English physicist, confirms the existence of neutrons, which have no charge. Atomic nuclei contain neutrons and positively charged protons.