Atomic Theory

Atomic Theory

1. Democritus

   • 4th century BC: proposed that the universe was made of indivisble units; atoms.
   • thought the movement of atoms caused the changes in matter that he observed.

2. Dalton

   • 1808: all atoms of a given element were exactly alike, and atoms of different elements could join to form compounds.
   • also believed that atoms could not be divided.

3. Thomson

   • 1897: his experiment suggested that cathode rays were made of negatively charged particles that came from inside atoms.
   • they showed that atoms can be divided into smaller parts.