Exam1A_Key - Rutherford calculated that the only way the...

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32. Explain how Ernest Rutherford and his coworkers discovered the atomic nucleus. (10 points) The nucleus was discovered via Rutherford’s famous Gold Foil Experiment. They bombarded a very thin gold foil with ± particles, which are high speed, positively charged particles thousands of times smaller than an atom. ± particles are given off by some radioactive materials. In the experiment, it was expected that the ± particles would pass through the thin gold foil with ease. People believed the gold atoms were made of very diffuse positive charge with electrons embedded throughout (the plum pudding model of the atom). The repulsive forces between the positive charge of the ± particle and the very diffuse positive charge within the gold atoms would be far too weak to deflect an ± particle if indeed the plum pudding model of the gold atoms were true. However, some ± particles were deflected by the gold, and a few (about 1 in each 8,000) bounced back off the gold in the direction from which they came!
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Unformatted text preview: Rutherford calculated that the only way the postive-positive repulsive forces could be large enough to stop an particle and send it back from where it came would be if the positive charge of the gold atoms were concentrated in one tiny, tiny area within the gold atom. He called this area the nucleus. He showed that all the positive charge of an atom and nearly all of its mass are concentrated in this tiny nucleus. Thus, most of the atom is just empty space containing the electrons. His nuclear model of the atom explained his experimental results beautifully. Most particles passed through the foil undetected because they passed through the empty space regions of the gold atoms. A few were deflected a bit because they came near a gold nucleus and the repulsion changed their direction of movement. And a very few, about 1 in 8,000, happened to hit a gold nucleus head on, thus being stopped and repelled back in the opposite direction....
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This note was uploaded on 06/21/2010 for the course CHEM 11 taught by Professor Scholefield during the Spring '08 term at Santa Monica.

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Exam1A_Key - Rutherford calculated that the only way the...

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