• Democritus
    400 BCE

    Democritus

    He theorized that all material bodies comprise indivisibly small “atoms.”
  • John Dalton

    John Dalton

    based on the concept that each element consists of its own unique brand of indivisible atom
  • JJ Thompson

    JJ Thompson

    discovery that atoms were made up of smaller components
  • Ernest Rutherford

    Ernest Rutherford

    Rutherford established that the mass of the atom is concentrated in its nucleus
  • Niels Bohr

    Niels Bohr

    proposed a model of the atom in which the electron was able to occupy only certain orbits around the nucleus
  • James Chadwick

    James Chadwick

    discovery of the neutron in the atom