Atomic Theory - Timeline

Democritus The Atom "Atomos" The atom could not be created, destroyed or further divided. Broke a shell until it could break no more.

Aristotle Matter is made of Earth, Wind, and Fire No Empty Space NO ATOMS

John Dalton Studied chemical reactions Studied mass ratios CREATED ATOMIC THEORY (Matter is made of atoms)

Sir William Crookes Used Cathode Ray Tubes to conduct experiments Accidentally discovered electrons (Negatively charged particles)

J.J. Thomson Used Cathode Ray Tubes to conduct experiments Determined ratio of charge to mass of an electron Thus discovering there were things smaller than an atom

Robert Millikan Used oil drop apparatus Discovered the exact charge of an electron (1.602 X10^19)

Ernest Rutherford Using gold foil in a tube Studied positively charged alpha particles DISCOVERED NUCLEUS Created plum pudding model