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How Rutherford Discovered
the proton: One of science’s
greatest experiments!
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.
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
Fluorescent Screen
gold foil & were not deflected
Fluorescent Screen
MOST went through
Alpha
Particles
empty space
Conclusions
from
Rutherford’s
Experiment:
FEW approach
nucleus & bounced
back
Gold Atom
3 Main Observations
SEVERAL were
deflected by the nucleus
OBSERVATIONS
1. MOST (almost all) went
through the gold foil &
were not deflected
2. FEW (not many)
bounced directly back
3. SEVERAL (some)
passed through the gold
foil & were deflected
CONCLUSIONS
Atom is mostly empty space
The atom’s dense core
(nucleus) must be very small
and positive
The nucleus must be positive
(law of repulsion)
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
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
1. Since most of the alpha particles went through the gold foil,
the atom consists of mostly of empty space.
2. All of the alpha particles are deflected because they repel
the electrons
3. Most of the alpha particles bounce straight back showing
that the nucleus is very large.
4. Several of the alpha particles are deflected showing that the
nucleus must have a positive charge

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
nucleus
bounced back- direct hit on