Transcript Rutherford’s experiment and model

Rutherford’s experiment
Day 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
Deconstructing Thomson’s 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 Thomson’s model?
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?
Rutherford’s experiment- online
• http://phet.colorado.edu/en/simulation/ruthe
rford-scattering
• Make sure to click “show traces”
• 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?
Rutherford’s 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!