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Chapter 29 Atoms and Molecules © 2010 Pearson Education, Inc. PowerPoint® Lectures for College Physics: A Strategic Approach, Second Edition 29 Atoms and Molecules © 2010 Pearson Education, Inc. Slide 29-2 © 2010 Pearson Education, Inc. Slide 29-3 © 2010 Pearson Education, Inc. Slide 29-4 © 2010 Pearson Education, Inc. Slide 29-5 Spectroscopy © 2010 Pearson Education, Inc. Slide 29-10 Continuous Spectra and Blackbody Radiation © 2010 Pearson Education, Inc. Slide 29-11 Discrete Spectra of the Elements © 2010 Pearson Education, Inc. Slide 29-12 The Hydrogen Spectrum Wavelengths of visible lines in the hydrogen spectrum Balmer’s formula 91.1 nm λ 1 1 2 2 m n © 2010 Pearson Education, Inc. Slide 29-13 Rutherford’s Experiment © 2010 Pearson Education, Inc. Slide 29-14 Using the Nuclear Model Ionization The nucleus © 2010 Pearson Education, Inc. Isotopes Slide 29-15 Bohr’s Model of Atomic Quantization © 2010 Pearson Education, Inc. Slide 29-16 Bohr’s Model of Atomic Quantization (cont’d) © 2010 Pearson Education, Inc. Slide 29-17 Frequencies of Photons Emitted in Electron Transitions Eatom fphoton h © 2010 Pearson Education, Inc. Slide 29-18 Representing Atomic States Energy-level diagram © 2010 Pearson Education, Inc. Slide 29-19 The Bohr Hydrogen Atom © 2010 Pearson Education, Inc. Slide 29-20 Energy-Level Diagram of the Hydrogen Atom © 2010 Pearson Education, Inc. Slide 29-21 The Quantum-Mechanical Hydrogen Atom 1. Schrödinger found that the energy of the hydrogen atom is given by the same expression found by Bohr, or En 13.60 eV n2 n 1, 2,3,... The integer n is called the principal quantum number. 2. The angular momentum L of the electron’s orbit must be one of the values L l (l 1) U l 0,1, 2,3,..., n 1 The integer l is called the orbital quantum number. © 2010 Pearson Education, Inc. Slide 29-22 The Quantum-Mechanical Hydrogen Atom (cont’d) 3. The plane of the electron’s orbit can be tilted, but only at certain discrete angles. Each allowed angle is characterized by a quantum number m, which must be one of the values m l , l 1,...,0,..., l 1, l The integer m is called the magnetic quantum number because it becomes important when the atom is placed in a magnetic field. 4. The electron’s spin can point only up or down. These two orientations are described by the spin quantum number ms, which must be one of the values 1 1 ms or 2 2 © 2010 Pearson Education, Inc. Slide 29-23 Energy and Angular Momentum of the Hydrogen Atom © 2010 Pearson Education, Inc. Slide 29-24 Energy Levels in Multielectron Atoms Hydrogen atom © 2010 Pearson Education, Inc. Multielectron atom Slide 29-25 Excited States and the Pauli Exclusion Principle Helium atom © 2010 Pearson Education, Inc. Lithium atom Slide 29-26 The Periodic Table © 2010 Pearson Education, Inc. Slide 29-27 Building Up the Periodic Table © 2010 Pearson Education, Inc. Slide 29-28 Excitation by Absorption and Collision © 2010 Pearson Education, Inc. Slide 29-29 Emission Spectra © 2010 Pearson Education, Inc. Slide 29-30 Checking Understanding Suppose that an atomic excited state decays to the ground state by emission of two photons, with energies E1 and E2. Is it possible for that excited state to decay to the ground state by emission of a single photon with energy E1 + E2? A. It is always possible, for every atom. B. It is never possible, for any atom. C. It is always possible for hydrogen atoms, but is unlikely for other atoms. © 2010 Pearson Education, Inc. Slide 29-31 Answer Suppose that an atomic excited state decays to the ground state by emission of two photons, with energies E1 and E2. Is it possible for that excited state to decay to the ground state by emission of a single photon with energy E1 + E2? A. It is always possible, for every atom. B. It is never possible, for any atom. C. It is always possible for hydrogen atoms, but is unlikely for other atoms. © 2010 Pearson Education, Inc. Slide 29-32 Molecules © 2010 Pearson Education, Inc. Slide 29-33 Fluorescence © 2010 Pearson Education, Inc. Slide 29-34 Checking Understanding Which of the following is not a possible fluorescence process? A. B. Absorption of red light and emission of green light Absorption of ultraviolet light and emission of infrared light C. Absorption of ultraviolet light and emission of green light D. Absorption of blue light and emission of red light © 2010 Pearson Education, Inc. Slide 29-35 Answer Which of the following is not a possible fluorescence process? A. Absorption of red light and emission of green light B. Absorption of ultraviolet light and emission of infrared light C. Absorption of ultraviolet light and emission of green light D. Absorption of blue light and emission of red light © 2010 Pearson Education, Inc. Slide 29-36 Stimulated Emission and Lasers © 2010 Pearson Education, Inc. Slide 29-37 Photon Amplification © 2010 Pearson Education, Inc. Slide 29-38 A Helium-Neon Laser © 2010 Pearson Education, Inc. Slide 29-39