How did we discover what's inside an atom? For centuries, atoms were thought to be indivisible. These key milestones changed our understanding of the fundamental building blocks of life and medicine.
Using a cathode ray tube, Thomson discovered that atoms contain tiny, negatively charged particles.
In his famous "Oil Drop" experiment, Millikan measured how microscopic oil droplets fell through an electric field.
Rutherford fired alpha particles at a thin sheet of gold foil. Most passed through, but some bounced back—a shocking result at the time.
[Image of the Rutherford gold foil experiment diagram]
The final pieces of the nuclear puzzle explained why atoms of the same element could have different weights.
| Particle | Charge | Mass (amu) | Location |
|---|---|---|---|
| Proton | Positive (+1) | ~1 | Inside Nucleus |
| Neutron | Neutral (0) | ~1 | Inside Nucleus |
| Electron | Negative (-1) | 0.0005 (Negligible) | Electron Cloud |