GeoMidterm3StudyGuide - Geol 130 MIII Study Guide Fall 2011...

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Geol 130 MIII Study Guide Fall 2011 The Nature of Matter Indirect evidence for atoms Gas Laws—PV=NRT Statistical Mechanics : Without being able to see atoms, scientists could still think about how atoms interacted using Newton’s Laws. Treat atoms as billiard balls and develop a mathematical method that can deal with large numbers of atom interactions and likelihood that interactions are random. Statistical mechanics can explain actions of gases. o Assume atoms exist and follow Newtonian mechanics to derive ideal gas law PV=NRT Direct evidence for atoms Einstein’s explanation of Brownian motion : The fact that inanimate objects, like pollen, appear to move in water as seen under a microscope. Einstein used statistical mechanics to show that the motion was due to individual water ‘atoms’ (actually molecules) hitting inanimate objects and moving them randomly through the water. Cathode rays : The normal way to heat up substances was to put them into a closed glass jar (bell jar) that is evacuated. Then an electric current is passed through the substance to heat it up (just like the electric stove burner). o Some metals, when heated in a vacuum, give off radiation that cannot penetrate the bell jar glass. o This ‘radiation’ cannot be light. o It was called cathode radiation or cathode rays. Thomson’s measurement of e/m : J.J. Thompson studied cathode rays by placing electric and magnetic ±elds around the edges of the bell jar and watched the effects. He showed that cathode rays could be deflected by electric ±elds. o From this he hypothesized that they were actually negatively charged particles. o Different metals all give the same cathode rays with the same ratio of charge to mass (e/m). We cannot actually measure mass of these particles, but we can measure the ratio of charge to mass by watching the change in path as electric ±eld strength is changed
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Thomson’s watermelon atom : There must be an equal number so that there is no net charge. The positive-charged ions and negative-charged electrons are interspersed inside the atom. o This has often been called the watermelon model with electrons being the black seeds. Milliken’s measurement of e : Uses an oil drop Discovery of the nucleus Gold foil alpha scattering : Rutherford shot alpha particles (ions) at this gold foil and noted that almost went through or caused ejection of electrons on impact. Why gold foil? It can be hammered very thin with the goal of reducing
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This note was uploaded on 12/08/2011 for the course GEOL 130Lxg at USC.

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GeoMidterm3StudyGuide - Geol 130 MIII Study Guide Fall 2011...

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