1. Subatomic Particles and the Nuclear Atom
Chapter 4
Section 2

2. The Electron The cathode ray was accidentally discovered.
It was a stream of negatively charged particles.
J.J. Thomson’s experiments with the cathode ray allowed him to determine that atoms contained electrons which were extremely small (1890s).

3. The Electron (cont.)
An American physicist, Robert Milliken (1909), discovered through experiment that electrons were negatively charged

4. The Nucleus
Rutherford (1911), began experimenting and discovered that Thomson’s model was incorrect.
This led to the discovery of the nucleus which is located in the center of the atom and is positively charged.
The nucleus also contains the majority of the mass.

5. Protons and Neutrons
Rutherford concluded that the nucleus contained positively charged particles called protons (1920).
In 1932, Rutherford’s coworker, James Chadwick showed that the nucleus also contained neutrally charged particles called neutrons.