1. The Gold Foil and the Nucleus
Rutherford
The Gold Foil and the Nucleus

2. Gold Foil Model

3. The J.J. Thomson Model “Plum Pudding Model”
The pudding was thought to be positively charged
The negatively charged “Plums” (electrons) were believed to be spread evenly throughout the atom

4. The Apparatus

5. What is an “Alpha Particle”
An alpha particle consists of 2 protons and 2 neutrons with a mass much greater than an electron

6. Observation
According to Thomson, the Alpha particles should have passed right through
When some of the particles bounced straight back, he concluded that there must be something with a much greater mass at the center of the atom!

7. The Outcome Rutherford's three observations:
Most alpha particles passed straight through the foil.
Some were deflected through angles less than 90 degrees.
A very small proportion of particles were deflected through angles greater than 90o.
His three subsequent conclusions:
Most of the atoms are empty space.
The alpha particles have an overall positive charge, forcing them to be repelled away from the metal atoms in the foil.
The atoms in the foil have a large, dense nucleus in their centers.

8. A New Atomic Model