Democritus (400 BC): matter consists of different arrangements of atoms and void. Different packings and scattering of the atoms lead to different properties of matter, such as hot/cold etc. Introduces a mechanical picture of the universe (no gods). Difference between atoms and molecules not made.
Plato: four-element theory with atoms of corresponding shape: Fire-Tetrahedron, Air-Octahedron, Earth-Cube, Water-Icosahedron. Motivates Heisenberg in 20th century to think about group theory, symmetry and atoms.
Have a look at http://en.wikipedia.org/wiki/Atomismhttp://en.wikipedia.org/wiki/Atomism.
