1. Rutherford Scattering Experiment
Atomic Structure
Rutherford Scattering Experiment

2. Background: Plum Pudding Model
Thomson discovers the electron.
Atoms electrically neutral and have e-’s.
Atom must contain equal # of __ charge.
His model: negative e- in spread out cloud of + charge, hence: plums in pudding.

3. Analogy to Rutherford’s Experiment
What would be seen from
the other side of the tent:

4. Analogy to Rutherford’s Experiment
What would be seen from
the other side of the tent:

5. Rutherford’s Plan to “See” Inside Atom

6. The Probe: Alpha (α) Particle
α particles are tiny compared to the Au target atoms and would fit __________!
α particles are positively charged (+2); would be __________ by concentrated +.
In a collision with a tiny electron, the path of the massive α particles would not be altered or changed.
Alpha particles are
He nuclei without the
electrons, hence +2 charge!

7. The Target: Gold (Au) Foil
Rutherford chose gold for two reasons:
1) Gold can be pounded into very ______
sheets
m thick
2) Gold atoms are very _______ compared to the alpha particles.

8. The Screen: to “see” the α particles
Coated screen around the foil with zinc sulfide
Alpha particle hits screen: flash of light can be seen through a microscope.

10. Expected Results
If the Plum Pudding Model was correct, α particles would pass through the gold atoms undeflected.
α particles would pass through diffuse + “pudding” (like a plane through a cloud).
α particles traveling too fast and too big to be attracted by e-

11. Actual Results

12. Link to Brian Cox Video Link to Rutherford Animation
Link to Video with equipment
Video clip with + charges

13. Rutherford’s Conclusions and Supporting Evidence (know these!)
Conclusion #1: Most of atom is __________
Evidence: small number of α particles were scattered. Most passed straight through the Au atoms undeflected.
Conclusion #2: Atom contains a tiny, dense ___________ charge (nucleus).
Evidence: α particles (+2) repelled by a _____ charge. Had to be concentrated positive charge to show large deflections.

14. If the nucleus of a hydrogen atom were scaled up to the size of golf ball, what would the average distance of the electron from nucleus be?

15. Ans: About 1 mile; on this picture the far left edge (approximately)