Rutherford Alpha Particle Scattering Experiment
Rutherford's alpha particle scattering experiment changed the
way we think of atoms.
Before the
experiment the best model of the atom was known as the Thomson
or "plum
pudding" model. The atom was believed to consist of a positive
material "pudding" with negative "plums" distributed
throughout.
Rutherford made 3 observations:
Most of the fast, highly charged alpha particles went whizzing straight
through undeflected. This was the expected result for all of the particles if
the plum pudding model was correct.
Some of the alpha particles were deflected back through large angles.
This was not expected.
A very small number of alpha particles were deflected backwards! This was
definitely not as expected. Rutherford later remarked "It was as
incredible as if you fired a 15-inch shell at a piece of tissue paper and it
came back at you!"
To explain these results a new model of the atom was needed.
In this model the positive material is concentrated in a small but
massive (lot of mass - not size) region called the nucleus. The negative
particles (electrons) must be around the outside preventing one atom from
trespassing on its neighbours space to complete this model. The diagram below
will help you to understand the results of the experiment.
No comments