1. Development of Atomic Models In 1897, J.J. Thompson discovered that matter, and thus atoms contain negatively charged particles which he called electrons. Since most objects are neutral, he deduced that there must be a mass of positive charge surrounded by negatively charged electrons. The following diagram represents the accepted model of the atom that was present from 1897 until 1911. http://en.wikipedia.org/wiki/Plum_pudding_model

2. In 1911 a New Zealand scientist by the name of Ernest Rutherford, working with graduate student assistants were about to collect data that would modify J.J. Thompson’s model of the atom. Rutherford had earlier discovered fairly large radioactive particles that had a positive charge, which were named alpha (  ) particles. education.jlab.org

3. Rutherford and his team shot these particles at a very thin piece of gold foil (approximately 250 atoms thick). On the other side of the gold foil was a zinc sulfide screen which glowed when hit by alpha particles. Model of Rutherford’s Apparatus A. Based on Thompson’s Model of the atom, make a hypothesis to what Rutherford and his team would have predicted would happen when the foil was hit with positively charged alpha particles. (put this in your notebook)

4. Click on the following link to observe an animation of Rutherford’s Experiment. http://micro.magnet.fsu.edu/electromag/java/rutherford/ OR http://www.wwnorton.com/college/chemistry/gilbert/tutorials/ch 3.htm

5. deflected angle  degrees number scattered 15.0132,000 22.527,300 30.07,800 37.53,300 45.01,457 60.0477 75.0211 10570 12052 13543 15033 Number of Alpha Particles Number of Alpha Particles Number of Alpha Particles Shot at Gold Foil Went Through Gold Foil Ricocheted to Source 264,000 263,967 33 Alpha Particle Data From Rutherford’s Experiment B. Observe the following data carefully along with the animation on the previous slide. What are 3 ways that the model of the structure of the atom could be changed from Thompson’s model. Explain why you made these conclusions. Write these in your notebook.

6. Rutherford was quoted about his discovery by saying about the results of the gold foil experiment: “It was quite the most incredible event that ever happened to me in my life. It was as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you!” C. Based on your observations of his data, explain what Rutherford’s Quote means. Place this in your notebook. For further reading about how the electron was discovered, click here. http://www.broadeducation.com/htmlDemos/AbsorbChem/HistoryAtom/page.htm