Atomic Model Development

By debbiemlane
  • 400 BCE

    Democritus

    Democritus
    Everything is composed of atoms, there is empty space that lies between each atom, and atoms are indestructible.
    He was correct that everything is made up of atoms, but incorrect that atoms are indivisible.

  • John Dalton

    John Dalton
    All matter is made of atoms, atoms are indivisible, all atoms of a given element are identical in mass and properties, compounds are formed by a combination of two or more different kinds of atoms.
    A chemical reaction is a rearrangement of atoms.

  • J.J. Thomson

    J.J. Thomson
    Demonstrated that cathode rays were negatively charged. He also studied positively charged particles in neon gas. He proposed a model of the atom which resembled plum pudding. The negative electrons represent the raisins the pudding and the dough contain the positive charge. He was correct that there were positive and negative charged in atoms but failed to recognize the positive charges in the atom as particles.

  • Hantaro Nagaoka

    Hantaro Nagaoka
    Nagaoka proposed that an atom had a positively charged center and then surrounding that center was a number of revolving electrons. Similarly to how the planet Saturn has rings.

  • Ernest Rutherford

    Ernest Rutherford
    Rutherford concluded that the atom consisted of a small, dense, positively charged nucleus in the center of the atom with negatively charged electrons surrounding it. Essentially, he discovered that atoms had a nucleus.

  • Niels Bohr

    Niels Bohr
    Bohr presents atoms having a small, positively charged nucleus that is surrounded by electrons that travel in circular orbits around the nucleus.

  • Werner Heisenberg & Erwin Schrodinger

    Werner Heisenberg & Erwin Schrodinger
    Erwin Schrödinger proposed the quantum mechanical model of the atom, which treats electrons as matter waves.
    The Heisenberg uncertainty principle states that we can't know both the energy and position of an electron. Therefore, as we learn more about the electron's position, we know less about its energy, and vice versa.

  • James Chadwick

    James Chadwick
    James Chadwick bombarded beryllium atoms with alpha particles. An unknown radiation was produced.Chadwick interpreted this radiation as being composed of particles with a neutral electrical charge and the approximate mass of a proton. This particle became known as the neutron.