Rutherford Scattering Experiment Atomic Structure Rutherford Scattering Experiment

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.

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

Rutherford’s Plan to “See” Inside Atom

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!

The Target: Gold (Au) Foil Rutherford chose gold for two reasons: 1) Gold can be pounded into very ______ sheets 0.0000005 m thick 2) Gold atoms are very _______ compared to the alpha particles.

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

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-

Actual Results

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.