Rutherford

1
Rutherfords experiment

• Day 2

2
Last time

• Discussion of early atomic model- the plum
  pudding model
• To refresh your memory
• Large slightly positive mass with tiny negative
  electrons in it

3
Deconstructing Thomsons model

• You have
• A source of alpha particles (positively charged)
• Some atoms of the same element (identical)
• Detection device (to see where your alpha
  particles went)
• How would you test Thomsons model?

4
Overview of the gold-foil experiment

• Hans Geiger and Ernest Marsden shot helium nuclei
  (alpha particles, 2 charge) at a very thin sheet
  of gold foil
• What do you think would happen, based on the
  plum pudding model?

5
Rutherfords experiment- online

• http//phet.colorado.edu/en/simulation/rutherford-
  scattering
• Make sure to click show traces

6

• 1) What effect does alpha particle speed have on
  repulsion?
• 2) What does the size of the neutron have on
  repulsion?
• 3) How does the relative proportion of protons
  to neutrons affect repulsion?

7
Rutherfords conclusions

• How did this experiment change perceptions of
  what an atom is?
• There is a nucleus with a positive charge (since
  the charge must be concentrated)
• Most of the atom is empty space!