1. How Rutherford Discovered the proton: One of science’s greatest experiments!

2. Rutherford’s Atomic Model
Rutherford used the ideas of radioactivity to carry out experiments to help him better define the atomic model.
His experiment involved:
Exploring matter by shooting radioactive alpha particles against thin sheets of metal.

3. SEVERAL particles pass through the
A FEW particles are sharply deflected
SEVERAL particles pass through the
gold foil & were slightly deflected
Alpha
Particle beam
Thin sheet of
Gold foil
Radium
in Lead Block
MOST particles passed through the
gold foil & were not deflected
Fluorescent Screen
Fluorescent Screen

4. Conclusions from Rutherford’s Experiment:
Alpha Particles
MOST went through empty space
Conclusions from Rutherford’s Experiment:
FEW approach nucleus & bounced back
Gold Atom
3 Main Observations
SEVERAL were deflected by the nucleus
OBSERVATIONS
CONCLUSIONS 1.
MOST (almost all) went through the gold foil & were not deflected
Atom is mostly empty space 2.
FEW (not many) bounced directly back
The atom’s dense core (nucleus) must be very small and positive 3.
SEVERAL (some) passed through the gold foil & were deflected
The nucleus must be positive (law of repulsion)

5. placed electrons orbiting,
Rutherford Model
Rutherford proposed
a new
model based
on his findings
and
Thomson's Model.
Rutherford’s Model
placed electrons orbiting,
like a cloud,
around a dense,
positively
charged nucleus.
Nucleus
Electrons

6. Example # 3
Rutherford’s famous gold foil experiment is shown below. Which of the four statements stated are true and which are false? (there can be more than one true!)
Lead Box
(Radio active substance)
Gold
Lead
Florescent Screen
Since most of the alpha particles went through the gold foil, the atom consists of mostly of empty space.
All of the alpha particles are deflected because they repel the electrons
Most of the alpha particles bounce straight back showing that the nucleus is very large.
Several of the alpha particles are deflected showing that the nucleus must have a positive charge T F F T

7. Key Points to Remember Rutherford’s Model
Be familiar with diagram of experiment
Know experiment results:
Particles go through - mostly empty space
Particles slightly deflected - same charge as nucleus so repelled
Particles bounced back- direct hit on nucleus