Atom

History of the Atom

  • Democritus
    400 BCE

    Democritus

    Father of modern atomic theory; five parts of his atomic theory including that elements are composed of atoms and that element’s atoms are identical in mass.
  • Aristotle
    300 BCE

    Aristotle

    Dismissed Democritus’ atom as “worthless.” Said that the four elements were earth, fire, air and water.
  • John Dalton

    John Dalton

    He was the first person to identify the possibility of an atom.
  • John Dalton's Indivisible, Solid Sphere Model

    John Dalton's Indivisible, Solid Sphere Model

  • J.J. Thomson

    J.J. Thomson

    Discovered the electron.
  • J.J. Thomson's Plum Pudding Model

    J.J. Thomson's Plum Pudding Model

  • R.A. Millikan

    R.A. Millikan

    Determined the charge and mass of an electron through the oil drop experiment.
  • Ernest Rutherford

    Ernest Rutherford

    Said that an atom has a small positive nucleus and the remainder is empty space through the gold foil experiment.
  • Ernest Rutherford's Nuclear Model

    Ernest Rutherford's Nuclear Model

  • Niels Bohr

    Niels Bohr

    Predicted that electrons travel in specified energy levels.
  • Niels Bohr's Planetary Model

    Niels Bohr's Planetary Model

  • Henry Moesley

    Henry Moesley

    He stated that the atomic number of an element is equal to the number of protons in the nucleus.
  • Louis de Broglie

    Louis de Broglie

    Worked with Einstein to determine that electrons were similar to particles and waves.
  • Werner Heisenberg

    Werner Heisenberg

    Came up with the “uncertainty principle”, which stated that it is impossible to determine the position and momentum of a particle at the same time.
  • Erwin Schrodinger

    Erwin Schrodinger

    Viewed electrons as a cloud and introduced wave mechanics as a model for the atom.
  • Erwin Schrodinger's Quantum Mechanical Model

    Erwin Schrodinger's Quantum Mechanical Model

  • James Chadwick

    James Chadwick

    Discovered the neutron.