Term
| What did Geiger and Marsden expect to find when they shot alpha particles at the gold foil? |
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Definition
| Geiger and Marsden expected to find that most of the alpha particles travel straight through the foil with little deviation, with the remainder being deviated by a percent or two. |
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Term
| Geiger and Marsden expected to find that most of the alpha particles travelled straight through the foil with little deviation, with the remainder being deviated by a percent or two. Why did they think this? |
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Definition
| This thinking was based on the theory that positive and negative charges were spread evenly within the atom and that only weak electric forces would be exerted on the alpha particles that were passing through the thin foil at high energy. |
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Term
| What did Geiger and Marsden find when they shot alpha particles at the gold foil? |
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Definition
| What they found, to their great surprise, was that while most of the alpha particles passed straight through the foil, a small percentage of them were deflected at very large angles and some were even backscattered. |
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Term
| What did Geiger and Marsden conclude from their experiment? |
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Definition
| Because alpha particles have about 8000 times the mass of an electron and impacted the foil at very high velocities, it was clear that very strong forces were necessary to deflect and backscatter these particles. |
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Term
| When they reported their findings to Rutherford what did he do with the findings? |
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Definition
| Rutherford explained this phenomenon with a revitalized model of the atom in which most of the mass was concentrated into a compact nucleus (holding all of the positive charge), with electrons occupying the bulk of the atom's space and orbiting the nucleus at a distance. With the atom being composed largely of empty space,it was then very easy to construct a scenario where most of the alpha particles passed through the foil, and only the ones that encountered a direct collision with a gold nucleus were deflected or scattered backwards |
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Term
| What relationship was there between Geiger and Marsden and Rutherford? |
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Definition
| Rutherford was the Professor in charge of the work the graduate student Geiger and undergraduate Marsden were doing at Manchester University. |
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Term
| What year did the experiment take place, and what year did Rutherford put forward his new model of the atom that explained the findings? |
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Definition
1909 - the experiment happened and 1911 was the year Rutherford put forward his theory - a long time interval to do the work of figuring out how to explain the findings!
(The year of the founding of our school!) |
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Term
| What model of the atom was 'in vogue' before Rutherford's new model? |
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Definition
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Term
| Who put forward the 'Plum Pudding' model of the atom? |
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Definition
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Term
| Who put forward the 'Plum Pudding' model of the atom? |
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Definition
J.J. Thomson - the man who discovered the electron! (Nobel prize for Physics for this in 1906)
[image] |
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Term
| Sketch a diagram of the Plum Pudding atom |
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Definition
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Term
| When did J.J. Thomson propose the Plum Pudding model of the atom? |
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Definition
| The plum pudding model was proposed in March, 1904 before the discovery of the atomic nucleus. |
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Term
| Describe the Plum Pudding model of the atom |
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Definition
| In this model, the atom is composed of electrons (which Thomson still called "corpuscles," though Stoney had proposed that atoms of electricity be called electrons in 1894), surrounded by a soup of positive charge to balance the electron's negative charge, like plums surrounded by pudding. The electrons (as we know them today) were thought to be positioned throughout the atom, but with many electron structures possible, particularly rotating rings. Instead of a soup, the atom was also sometimes said to have had a cloud of positive charge. |
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Term
| It was quite the most incredible event that ever happened to me in my life. It was almost as incredible as if you had fired a 15-inch shell at a piece of tissue paper and it came back and hit you. - What was Rutherford talking about? |
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Definition
| No one imagined that in the centre of the atom there would be an intense positive electric field from a tiny compact nucleus that would repel alpha particles back the way the came! |
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Term
| Why did the alpha particles get backscattered by the gold nucleus? |
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Definition
Some people think they get backscattered because they hit the nucleus and bounced off... that is not the case - they actually got repelled because of their positive charge and the high concentrated positive charge of the gold nucleus - they come to a stop BEFORE they make contact!
[image]
From http://www.regentsprep.org/regents.cfm |
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