1. Elements & Atoms
Atomic theory grew as a series of models that developed from experimental evidence. As more evidence was collected, the theory and models were revised.

2. Elements & Atoms
Dalton Model – atoms are like smooth, hard balls that could not be broken into smaller pieces. (See p. 8 – Summary of Dalton’s Ideas)
Solid Sphere Model or Billiard Ball Model proposed by John Dalton

3. Elements & Atoms
Thomson Model – atoms have negatively charged electrons embedded in a positive charge.
Plum Pudding Model or Raisin Bun Model proposed by J.J. Thomson

4. Elements & Atoms
Rutherford’s Gold Foil Experiment – most particles pass through foil in straight line, but a few were strongly deflected. This led to proposal of Rutherford Model, small, positively charged nucleus in center of the atom.
Rutherford Model of a lithium atom.

5. Elements & Atoms
Bohr’s Model – electrons move in specific orbits around the nucleus of an atom.
The Bohr atom

6. Elements & Atoms
Cloud Model – electrons move rapidly in every direction around the nucleus.

7. Elements & Atoms
Modern Atomic Model – nucleus, which contains both protons and neutrons, is surrounded by a cloudlike region of electrons.