Outcomes

Student should be able to describe and compare the Plum Pudding model and the Rutherford model of the atom.
Students should recall that like charges repel and opposite charges attract.
Using the observations from the Geiger and Marsden’s experiment they should be able to make conclusions about the structure of the atom and how they support the Rutherford model.
To understand the factors (charge and speed) which affect the deflection of alpha particles by a nucleus.

Specification References

7.15 Describe the results of Geiger and Marsden’s experiments with gold foil and alpha particles
7.16 Describe Rutherford’s nuclear model of the atom and how it accounts for the results of Geiger and Marsden’s experiment and understand the factors (charge and speed) which affect the deflection of alpha particles by a nucleus.

Help students recall that like charges repel and unlike charges attract. Think about using the demo from identifying forces.
Teacher must state that the alpha particles are positively charged.
Introduce the plum pudding model
Introduce the Alpha scattering experiment, discuss the experimental set-up (the vacuum, alpha source, lead casing, phophorus screen etc..) and predict what would happen when alpha particles are fired at atoms based on the plum pudding model.
Use the 'Plum pudding model box' and the 'Rutherford model box' to simulate the experiment. Start with the ‘dilute positive sphere' in the 'Plum pudding model box', explaining that this is what they expected to see and then move onto the 'Rutherford model box'. These should be done undercover, the boxes should not be lifted. Students should only observe the results.
Emphasise the observations as a class and then split them into groups and using the observations and conclusions sheet they could try to draw a conclusion on the structure of the atom.

Remove the box and review the conclusions made
Ask the pupils to predict what would happen to the path of deflection of the alpha particle if the speed of the alpha particle is changed. Using the ramp shoot 'fast alpha particles' and 'slow alpha particles' at the Potential Hill. Were their predictions correct? Discuss
Extension- How would the charge of the nucleus or the target particle affect the path of deflection? Two sized potential hills would be needed here to demonstate this.

Write a dialogue between two people explaining the plum pudding and Rutherford models, the alpha scattering experiment and how their observations led to the Rutherford model of the atom.

Dialogue sheet on Radioactivity
Plum pudding sheet
Alpha scattering experiment sheet
One Ramp
Set of metal balls
One Rutherford model and one ‘dilute positive charge’ drawn on a piece of paper with two boxes to go over top. Boxes must have slits along base to allow ball to travel through.
Observations and conclusions sheet
Two sizes of potential hills or lycra sheet with middle pulled upward by different amounts?