Atomic Model Notes

Dalton's particles - 1803

  1. Atoms = small indestructible, indivisible particles.
  2. Atoms of an element are identical.
  3. Atoms of different elements are different.
  4. Atoms do not change their identity during chemical reactions.

Thompson's Plum Pudding - 1897

  1. Atom is made of smaller particles!
  2. Atom is uniform sphere with e- scattered throughout.

Curie's Radioactivity - 1897

  1. Becquerel and the Curies (France).
  2. Radioactivity : energy spontaneously emitted by elements.
  3. Rutherford (1899) discovers α and β particles.

Rutherford's Nucleus - 1910

  1. Observations by Rutherford's (and Geiger) experiment with α-particle, gold foil target and ZnS screen.
  2. Inference: + charge concentrated in a small, dense nucleus.

Bohr Model - 1913

  1. e- exist in discrete energy states.
  2. Energy states represented as levels around nucleus.
    1. First level can contain two e-
    2. Second, third and fourth levels can contain eight e-
    3. Lower levels are filled before upper levels.
    4. Levels can hold fewer than the maximum e-.
    5. More sophisticated model has sub-levels in each level. Identified with letters: s, p, d, f
  3. e- can absorb or emit energy and change their levels.
  4. Hydrogen Bohr radius = 5.29 x 10-11 m.

Quantum-Mechanic Model - 1926

  1. Work of Einstein and others showed that energy is the same as matter.
  2. Both can behave as particles and waves.
  3. Described with complex mathematics.
  4. e- described as moving in the electron cloud.
  5. Quantum numbers describe the atom's energy state: size, shape and orientation of e- field.