Atomic Model Notes
Dalton's particles - 1803
- Atoms = small indestructible, indivisible particles.
- Atoms of an element are identical.
- Atoms of different elements are different.
- Atoms do not change their identity during chemical reactions.
Thompson's Plum Pudding - 1897
- Atom is made of smaller particles!
- Atom is uniform sphere with e- scattered throughout.
Curie's Radioactivity - 1897
- Becquerel and the Curies (France).
- Radioactivity : energy spontaneously emitted by elements.
- Rutherford (1899) discovers α and β particles.
Rutherford's Nucleus - 1910
- Observations by Rutherford's (and Geiger) experiment with α-particle, gold foil target and ZnS screen.
- Inference: + charge concentrated in a small, dense nucleus.
Bohr Model - 1913
- e- exist in discrete energy states.
- Energy states represented as levels around nucleus.
- First level can contain two e-
- Second, third and fourth levels can contain eight e-
- Lower levels are filled before upper levels.
- Levels can hold fewer than the maximum e-.
- More sophisticated model has sub-levels in each level. Identified with letters: s, p, d, f
- e- can absorb or emit energy and change their levels.
- Hydrogen Bohr radius = 5.29 x 10-11 m.
Quantum-Mechanic Model - 1926
- Work of Einstein and others showed that energy is the same as matter.
- Both can behave as particles and waves.
- Described with complex mathematics.
- e- described as moving in the electron cloud.
- Quantum numbers describe the atom's energy state: size, shape and orientation of e- field.