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© 2007 Pearson Prentice Hall This work is protected by United States copyright laws and is provided solely for the use of instructors in teaching their courses and assessing student learning. Dissemination or sale of any part of this work (including on the World Wide Web) will destroy the integrity of the work and is not permitted. The work and materials from it should never be made available to students except by instructors using the accompanying text in their classes. All recipients of this work are expected to abide by these restrictions and to honor the intended pedagogical purposes and the needs of other instructors who rely on these materials. Clicker Questions ConcepTests Chapter 31 Physics, 3 rd Edition James S. Walker

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ConcepTest 31.1Ionization ConcepTest 31.1 Ionization How much energy does it take to ionize a hydrogen atom in its ground state? 1) 0 eV 2) 13.6 eV 3) 41.2 eV 4) 54.4 eV 5) 108.8 eV

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The energy of the ground state is the energy that binds the electron to the nucleus. Thus, an amount equal to this binding energy must be supplied in order to kick the electron out of the atom. ConcepTest 31.1Ionization ConcepTest 31.1 Ionization How much energy does it take to ionize a hydrogen atom in its ground state? 1) 0 eV 2) 13.6 eV 3) 41.2 eV 4) 54.4 eV 5) 108.8 eV Follow-up: How much energy does it take to change a He + ion into a He ++ ion? Keep in mind that Z = 2 for helium.

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ConcepTest 31.2aAtomic Transitions I n = 1 n = 2 n = 3 n = 5 n = 4 1) 2 5 2) 5 3 3) 8 5 4) 4 7 5) 15 7 For the possible transitions shown, for which transition will the electron gain the most energy?

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ConcepTest 31.2aAtomic Transitions I n = 1 n = 2 n = 3 n = 5 n = 4 1) 2 5 2) 5 3 3) 8 5 4) 4 7 5) 15 7 higher higher n The electron must go to a higher orbit (higher n) in order for the electron to gain energy. Because of the 1/n 2 dependence: E 2 – E 5 > E 4 – E 7 For the possible transitions shown, for which transition will the electron gain the most energy? Follow-up: Which transition will emit the shortest wavelength photon?

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n = 1 n = 2 n = 3 n = 5 n = 4 n = n = 6 The Balmer series for hydrogen can be observed in the visible part of the spectrum. Which transition leads to the reddest line in the spectrum? 1) 3 2 2) 4 2 3) 5 2 4) 6 2 5) 2 ConcepTest 31.2bAtomic Transitions II

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3 2 lowest energylowest frequency longest wavelength reddest The transition 3 2 has the lowest energy and thus the lowest frequency photon, which corresponds to the longest wavelength (and therefore the “reddest”) line in the spectrum. n = 1 n = 2 n = 3 n = 5 n = 4 n = n = 6 The Balmer series for hydrogen can be observed in the visible part of the spectrum. Which transition leads to the reddest line in the spectrum? 1) 3 2 2) 4 2 3) 5 2 4) 6 2 5) 2 ConcepTest 31.2bAtomic Transitions II Follow-up: Follow-up: Which transition leads to the shortest wavelength photon?

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ConcepTest 31.3Balmer Series When a broad spectrum of light passes through hydrogen gas at room temperature, absorption lines are observed that correspond only to the Balmer (n f = 2) series. Why aren’t other series observed? 1) they’re there, but they’re invisible 2) only the Balmer series can be excited at room temperature 3) the other series have been ionized 4) all the photons have been used up

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ConcepTest 31.3Balmer Series When a broad spectrum of light passes through hydrogen gas at room temperature, absorption lines are observed that correspond only to the Balmer (n f = 2) series. Why aren’t other series observed? 1) they’re there, but they’re invisible 2) only the Balmer series can be excited at room temperature 3) the other series have been ionized 4) all the photons have been used up wavelengths in the visible part The Balmer series is the only one that involves wavelengths in the visible part of the spectrum! Follow-up: Follow-up: From the diagram at right, where in the EM spectrum is the Lyman series located?

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ConcepTest 31.4aEnergy Levels I n = 1 n = 2 n = 3 n = 5 n = 4 Suppose there is an atom that contains exactly five energy levels. How many different transitions are possible? (Count only one direction!) 1) 4 2) 5 3) 10 4) 20 5) many more than 20

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ConcepTest 31.4aEnergy Levels I n = 1 n = 2 n = 3 n = 5 n = 4 upward Just count them! Transitions upward: n = 1 n = ? 4 transitions n = 2 n = ? 3 transitions n = 3 n = ? 2 transitions n = 4 n = ? 1 transition This gives a total of 10 possible ones This gives a total of 10 possible ones. Suppose there is an atom that contains exactly five energy levels. How many different transitions are possible? (Count only one direction!) 1) 4 2) 5 3) 10 4) 20 5) many more than 20

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(1)(2)(3)(4) The emission spectrum for the atoms of a gas is shown. Which of the energy level diagrams below corresponds to this spectrum? ConcepTest 31.4bEnergy Levels II

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(1)(2)(3)(4) transition 6 transitionsfour levels The two transitions between the closely spaced levels have less energy, while the other four have larger energies Each line in the spectrum corresponds to a transition between energy levels! Since there are 6 transitions shown, there must be four levels. The two transitions between the closely spaced levels have less energy, while the other four have larger energies. The emission spectrum for the atoms of a gas is shown. Which of the energy level diagrams below corresponds to this spectrum? ConcepTest 31.4bEnergy Levels II

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ConcepTest 31.5Rutherford Model Suppose the Rutherford model was correct (instead of the Bohr model). What would the absorption spectrum of a hydrogen atom look like? 1) there would be no change 2) the absorption lines would be broader 3) it would be completely black 4) the absorption lines would be shifted 5) the absorption lines would be bright instead of dark

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all orbits are allowed all In the Rutherford model, all orbits are allowed for the electrons. Thus, the atom would be able to absorb all wavelengths of light instead of only the specific ones allowed in the Bohr model. ConcepTest 31.5Rutherford Model Suppose the Rutherford model was correct (instead of the Bohr model). What would the absorption spectrum of a hydrogen atom look like? 1) there would be no change 2) the absorption lines would be broader 3) it would be completely black 4) the absorption lines would be shifted 5) the absorption lines would be bright instead of dark

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