Democritus (440 BC)
Developed the concept of the “atom” which is Greek for not able to be divided. Can you keep dividing something in half forever?
2. Aristotle (also around 440 BC)
Disagreed with Democritus and thought that the atom was the smallest particle into which an element could be divided and still be the same substance.
3. Dalton (1803)
All substances are made of atoms. Atoms cannot be created, divided or destroyed. Atoms of the same element are exactly alike.
Atoms join with other atoms to make new substances (compounds).
4. Thompson (1897)
Discovered that there are small particles inside an atom named electrons (negatively charged), so atoms can be divided further.
5. Rutherford (1909)
Theorized that atoms must be mostly empty space with a high density center (nucleus with a positive charge)
6. Bohr (1913)
Theorized that electrons move around in certain paths or energy levels.
7. Modern Atomic Theory (Schrodinger and Heisenberg)
States that electrons don’t travel in predictable paths, but there are regions called electron clouds where electrons are likely to be found.