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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 Reading Quiz Answer 1. What is the “Balmer formula” a formula for? 1. What is the “Balmer formula” a formula for? A. B. C. D. Masses of atomic nuclei of hydrogen isotopes Wavelengths in the hydrogen emission spectrum Energies of stationary states of hydrogen Probabilities of electron position in stationary states of hydrogen © 2010 Pearson Education, Inc. Slide 29-6 A. B. C. D. Masses of atomic nuclei of hydrogen isotopes Wavelengths in the hydrogen emission spectrum Energies of stationary states of hydrogen Probabilities of electron position in stationary states of hydrogen © 2010 Pearson Education, Inc. Slide 29-7 1 Reading Quiz Answer 2. Which of the following aspects of the stationary states of hydrogen does Bohr’s analysis of the hydrogen atom get right? 2. Which of the following aspects of the stationary states of hydrogen does Bohr’s analysis of the hydrogen atom get right? A. B. C. D. The existence of a “spin” quantum number The existence of a “magnetic” quantum number The shapes of the electron clouds The energies of the stationary states © 2010 Pearson Education, Inc. A. B. C. D. Slide 29-8 Spectroscopy © 2010 Pearson Education, Inc. The existence of a “spin” quantum number The existence of a “magnetic” quantum number The shapes of the electron clouds The energies of the stationary states Slide 29-9 © 2010 Pearson Education, Inc. Continuous Spectra and Blackbody Radiation Slide 29-10 Discrete Spectra of the Elements Slide 29-11 © 2010 Pearson Education, Inc. The Hydrogen Spectrum Wavelengths of visible lines in the hydrogen spectrum Balmer’s formula l = © 2010 Pearson Education, Inc. Slide 29-12 © 2010 Pearson Education, Inc. 91.1 nm ⎛ 1 1⎞ ⎜ 2− 2⎟ ⎝m n ⎠ Slide 29-13 2 Rutherford’s Experiment Using the Nuclear Model Ionization The nucleus Slide 29-14 © 2010 Pearson Education, Inc. Bohr’s Model of Atomic Quantization Frequencies of Photons Emitted in Electron Transitions fphoton = © 2010 Pearson Education, Inc. © 2010 Pearson Education, Inc. Slide 29-15 Bohr’s Model of Atomic Quantization (cont’d) Slide 29-16 © 2010 Pearson Education, Inc. Isotopes © 2010 Pearson Education, Inc. Slide 29-17 Representing Atomic States Energy-level diagram ΔEatom h Slide 29-18 © 2010 Pearson Education, Inc. Slide 29-19 3 The Bohr Hydrogen Atom Energy-Level Diagram of the Hydrogen Atom Slide 29-20 © 2010 Pearson Education, Inc. Slide 29-21 © 2010 Pearson Education, Inc. The Quantum-Mechanical Hydrogen Atom The Quantum-Mechanical Hydrogen Atom (cont’d) 1. Schrödinger found that the energy of the hydrogen atom is given by the same expression found by Bohr, or 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 En = − 13.60 eV n2 n = 1, 2,3,... m = −l , −l + 1,...,0,..., l − 1, l 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 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 The integer l is called the orbital quantum number. ms = − © 2010 Pearson Education, Inc. Slide 29-22 Energy and Angular Momentum of the Hydrogen Atom © 2010 Pearson Education, Inc. Slide 29-24 1 1 or + 2 2 Slide 29-23 © 2010 Pearson Education, Inc. Energy Levels in Multielectron Atoms Hydrogen atom © 2010 Pearson Education, Inc. Multielectron atom Slide 29-25 4 Excited States and the Pauli Exclusion Principle Helium atom © 2010 Pearson Education, Inc. Slide 29-26 © 2010 Pearson Education, Inc. Slide 29-27 Excitation by Absorption and Collision Building Up the Periodic Table © 2010 Pearson Education, Inc. The Periodic Table Lithium atom Slide 29-28 Emission Spectra © 2010 Pearson Education, Inc. Slide 29-29 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 C. i always l possible ibl ffor h hydrogen d atoms, t b butt iis unlikely for other atoms. © 2010 Pearson Education, Inc. Slide 29-30 © 2010 Pearson Education, Inc. Slide 29-31 5 Answer Molecules 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 C. i always l possible ibl for f hydrogen h d atoms, t but b t is i unlikely for other atoms. © 2010 Pearson Education, Inc. Slide 29-32 Fluorescence © 2010 Pearson Education, Inc. Slide 29-33 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 29-34 Answer © 2010 Pearson Education, Inc. Slide 29-35 Stimulated Emission and Lasers 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 © 2010 Pearson Education, Inc. Slide 29-37 6 Photon Amplification © 2010 Pearson Education, Inc. A Helium-Neon Laser Slide 29-38 © 2010 Pearson Education, Inc. Slide 29-39 7