29 Atoms and Molecules

Transcription

1 29 Atoms and Molecules Slide 29-2 Slide 29-3 Slide 29-4 Slide 29-5 Reading Quiz 1. What is the Balmer formula a formula for? A. Masses of atomic nuclei of hydrogen isotopes B. Wavelengths in the hydrogen emission spectrum C. Energies of stationary states of hydrogen D. Probabilities of electron position in stationary states of hydrogen Answer 1. What is the Balmer formula a formula for? A. Masses of atomic nuclei of hydrogen isotopes B. Wavelengths in the hydrogen emission spectrum C. Energies of stationary states of hydrogen D. Probabilities of electron position in stationary states of hydrogen Slide 29-6 Slide

2 Reading Quiz 2. Which of the following aspects of the stationary states of hydrogen does Bohr s analysis of the hydrogen atom get right? A. The existence of a spin quantum number B. The existence of a magnetic quantum number C. The shapes of the electron clouds D. The energies of the stationary states Answer 2. Which of the following aspects of the stationary states of hydrogen does Bohr s analysis of the hydrogen atom get right? A. The existence of a spin quantum number B. The existence of a magnetic quantum number C. The shapes of the electron clouds D. The energies of the stationary states Slide 29-8 Slide 29-9 Spectroscopy Continuous Spectra and Blackbody Radiation Slide Slide Discrete Spectra of the Elements The Hydrogen Spectrum Wavelengths of visible lines in the hydrogen spectrum Balmer s formula 91.1 nm l = m n Slide Slide

3 Rutherford s Experiment Using the Nuclear Model Ionization The nucleus Isotopes Slide Slide Bohr s Model of Atomic Quantization Bohr s Model of Atomic Quantization (cont d) Slide Slide Frequencies of Photons Emitted in Electron Transitions Representing Atomic States Energy-level diagram f photon ΔE = h atom Slide Slide

4 The Bohr Hydrogen Atom Energy-Level Diagram of the Hydrogen Atom Slide Slide 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 ev = n= 1,2,3,... n2 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. 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 m s, which must be one of the values 1 1 m s = or Slide Slide Energy and Angular Momentum of the Hydrogen Atom Energy Levels in Multielectron Atoms Hydrogen atom Multielectron atom Slide Slide

5 Excited States and the Pauli Exclusion Principle Helium atom Lithium atom The Periodic Table Slide Slide Building Up the Periodic Table Excitation by Absorption and Collision Slide Slide Emission Spectra 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 E 1 + E 2? 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. Slide Slide

6 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 E 1 + E 2? Molecules 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. Slide Slide Fluorescence Checking Understanding 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 Slide Slide Answer Which of the following is not a possible fluorescence process? Stimulated Emission and Lasers 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 Slide Slide

7 Photon Amplification A Helium-Neon Laser Slide Slide