Chapter 42 - 42 Atomic Physics CHAPTER OUTLINE 42.1 42.2...

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42 CHAPTER OUTLINE 42.1 Atomic Spectra of Gases 42.2 Early Models of the Atom 42.3 Bohr’s Model of the Hydrogen Atom 42.4 The Quantum Model of the Hydrogen Atom 42.5 The Wave Functions of Hydrogen 42.6 Physical Interpretation of the Quantum Numbers 42.7 The Exclusion Principle and the Periodic Table Visible and X-ray 42.8 More on Atomic Spectra: Spontaneous and 42.9 Stimulated Transitions 42.10 Lasers Atomic Physics ANSWERS TO QUESTIONS Q42.1 Neon signs emit light in a bright-line spectrum, rather than in a continuous spectrum. There are many discrete wavelengths which correspond to transitions among the various energy levels of the neon atom. This also accounts for the particular color of the light emitted from a neon sign. You can see the separate colors if you look at a section of the sign through a diffraction grating, or at its reflection in a compact disk. A spectroscope lets you read their wavelengths. Q42.2 One assumption is natural from the standpoint of classical physics: The electron feels an electric force of attraction to the nucleus, causing the centripetal acceleration to hold it in orbit. The other assumptions are in sharp contrast to the behavior of ordinary-size objects: The electron’s angular momentum must be one of a set of certain special allowed values. During the time when it is in one of these quantized orbits, the electron emits no electromagnetic radiation. The atom radiates a photon when the electron makes a quantum jump from one orbit to a lower one. Q42.3 If an electron moved like a hockey puck, it could have any arbitrary frequency of revolution around an atomic nucleus. If it behaved like a charge in a radio antenna, it would radiate light with frequency equal to its own frequency of oscillation. Thus, the electron in hydrogen atoms would emit a continuous spectrum, electromagnetic waves of all frequencies smeared together. Q42.4 (a) Yes—provided that the energy of the photon is precisely enough to put the electron into one of the allowed energy states. Strangely—more precisely non-classically—enough, if the energy of the photon is not sufficient to put the electron into a particular excited energy level, the photon will not interact with the atom at all! (b) Yes—a photon of any energy greater than 13.6 eV will ionize the atom. Any “extra” energy will go into kinetic energy of the newly liberated electron. Q42.5 An atomic electron does not possess enough kinetic energy to escape from its electrical attraction to the nucleus. Positive ionization energy must be injected to pull the electron out to a very large separation from the nucleus, a condition for which we define the energy of the atom to be zero. The atom is a bound system. All this is summarized by saying that the total energy of an atom is negative.
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Chapter 42 - 42 Atomic Physics CHAPTER OUTLINE 42.1 42.2...

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