Instructors_Guide_Ch41 - 41 Atomic Physics Recommended...

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41 Atomic Physics Recommended class days: 3 Background Information The final two chapters are the culmination of elementary quantum physics. The level of presentation is higher than in other introductory texts, because students have learned some basic ideas about wave functions, but lower than in a modern physics course. This chapter on atomic physics provides an important wrap-up to the story line about the atomic structure of matter, and it resolves previously introduced issues about spectra and the difference between absorption and emission spectra. In addition, students find the information about lasers to be quite interesting. The Bohr model of the atom introduced the idea of stationary states, but the Bohr model was an ad hoc hypothesis and not a complete theory. Consequently, Bohr was unable to determine the stationary states of any atom other than hydrogen. Quantum mechanics is a theory of the behavior of matter at the atomic scale. It is important for students to understand that: • Quantum mechanics does predict the stationary states of atoms correctly. • These successful predictions, among many others, are the tests by which we believe that quantum mechanics is the correct theory of atomic structure. Most students have learned rules about electron configurations in their chemistry classes, so many of the ideas in this chapter are not new to them. However, introductory chemistry provides no explanation or justification of the rules. Although we aren’t going to solve the Schrödinger equation for hydrogen in this course, students have seen enough quantum mechanics to recognize and understand that the quantum numbers are associated with finding the allowable wave functions. We can then use a graphical presentation of the wave functions to motivate the ideas of the shell model of atomic structure. The presentation is straightforward, not too detailed, and should present no formidable challenges to students. The one known area of difficulty is with regard to atomic excitation. Instructors take it for granted that atoms can be excited via inelastic collisions with electrons or other atoms. Many students don’t recognize this possibility unless it is pointed out explicitly. Most will need a few practice exercises to think about energy conservation in such collisions, to recog- nize how the atom responds by emitting one or more photons, and to see that the l selection rule of photon absorption does not apply to collisions. An important point to emphasize in contrasting collisional excitation with absorption is that the absorbed photon disappears but the collision partner does not. 41-1
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41-2 Instructor’s Guide Student Learning Objectives • To interpret the quantum-mechanical solution of the hydrogen atom. • To understand the basis for the shell model of atoms.
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Instructors_Guide_Ch41 - 41 Atomic Physics Recommended...

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