40_bohr - Lesson 40: Bohr's Model While Rutherford was...

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Lesson 40: Bohr's Model While Rutherford was working in his lab at the University of Manchester trying to figure out atoms, he had a person named Niels Bohr working for him. Previously Bohr had worked for J.J. Thomson. Bohr showed that he was a better than average physicists by suggesting multiple improvements to the experiments being done in Rutherford's lab. Eventually Bohr was even able to suggest an answer to the problem with Rutherford's Planetary model. Bohr was able to take two ideas and put them together to come up with his model. 1. Rutherford's Planetary Model Bohr knew that he couldn't completely trash Rutherford's Planetary model. The experiments Rutherford had done proved that there must be a positive nucleus surrounded by negative electrons. The change Bohr came up with concerned the electrons' positions. Rather than allowing the electrons to be just anywhere, he suggested that the could only exist at specific distances from the nucleus. 2. Quantum Mechanics' Discrete Energy Specific positions for the electrons agreed nicely with the ideas of discrete amounts of energy that we learned about in quantum mechanics. As we learned in the last lesson, if the electrons were anywhere they would eventually spiral in and crash. In fact, as they spiral in they should go faster and faster and release their energy in ever increasing amounts. Since E = hf, this would mean we should see a bunch of increasingly higher frequencies of EMR being given off by atoms all the time. But we don't. Instead, experiments showed that atoms only ever emit energy at specific frequencies. This must mean that specific, discrete amounts of energy are being emitted. Spectroscopy There was strong evidence of energy being released as quanta when physicists studied spectroscopy . This was one of Bohr's inspirations to come up with his model, as well as some of its best support. Spectroscopy involves looking at light from various sources through a diffraction grating and analyzing the colors that are seen. Emission Spectra In experiments it was discovered that if a high voltage (or heat) is applied to a gas sample of an element in a tube at low pressure, it will give off light. When a spectroscope is used to examine the light, it does not emit a
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This note was uploaded on 12/02/2011 for the course PHYSICS 235 taught by Professor Staff during the Fall '08 term at Rutgers.

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40_bohr - Lesson 40: Bohr's Model While Rutherford was...

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