* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Modern Physics 3-Atomic Physics
Geiger–Marsden experiment wikipedia , lookup
Double-slit experiment wikipedia , lookup
Renormalization wikipedia , lookup
Elementary particle wikipedia , lookup
James Franck wikipedia , lookup
Matter wave wikipedia , lookup
X-ray photoelectron spectroscopy wikipedia , lookup
Quantum electrodynamics wikipedia , lookup
Bohr–Einstein debates wikipedia , lookup
Particle in a box wikipedia , lookup
Wave–particle duality wikipedia , lookup
X-ray fluorescence wikipedia , lookup
Tight binding wikipedia , lookup
Electron scattering wikipedia , lookup
Rutherford backscattering spectrometry wikipedia , lookup
Atomic orbital wikipedia , lookup
Theoretical and experimental justification for the Schrödinger equation wikipedia , lookup
Electron configuration wikipedia , lookup
3/10/2015 Modern Physics 3 Atomic Physics-ch27 Physics 116 Eyres Dalton model: Atom as billiard ball • In 1803, John Dalton proposed a billiard ball model that viewed the atom as a small solid sphere. • According to Dalton, a sample of a pure element was composed of a large number of atoms of a single kind. • Each atom, regardless of type, contains an equal amount of positively and negatively charged subcomponents so that each atom is electrically neutral. © 2014 Pearson Education, Inc. 1 3/10/2015 Thomson model: Atom as plum pudding • In 1897, J. J. Thomson hypothesized that electrons were the negatively charged components of atoms. • In his model, an atom was similar to a spherically shaped plum pudding. © 2014 Pearson Education, Inc. Rutherford model: Atom as planetary system • In 1909, Ernest Rutherford and his postdoctoral colleague Hans Geiger hypothesized that the atom's mass was not spread uniformly throughout the atom, but instead concentrated in a small region. • Rutherford developed a new model of the atom in which a tiny nucleus contained nearly all of the mass of the atom and all of its positive charge. © 2014 Pearson Education, Inc. 2 3/10/2015 A difficulty with the planetary model • An accelerating electron emits electromagnetic radiation, and this radiation has energy. • Because the electron orbiting the nucleus is continually accelerating, the electron-nucleus system should continuously lose energy. • The Rutherford model could not explain the stability of atoms. © 2014 Pearson Education, Inc. Spectra of low-density gases and the need for a new model • Observations show that different gases produce different sets of spectral lines. • Scientists could not explain where the lines came from. © 2014 Pearson Education, Inc. 3 3/10/2015 Spectra of low-density gases and the need for a new model • In 1885, Johann Balmer found a pattern in the wavelengths of the visible spectral lines produced by hydrogen and represented it with the following equation: © 2014 Pearson Education, Inc. Bohr's model of the atom: Quantized orbits • In 1913, Danish physicist Niels Bohr developed a new model that explained the line spectra and the stability of the atom. • The structure of Rutherford's model, but imposed a restriction on the electron orbits. • The atom is made up of a small nucleus and an orbiting electron. • The electron can occupy only certain orbits, n. • When in these orbits, the electron does not radiate electromagnetic waves. • When an electron transitions from one stable orbit to another, the atom's energy changes. • When the energy of the atom decreases, the atom emits a photon. • To increase, the atom must absorb some energy, often a photon. • Because the stable orbits are discrete, the atom can radiate or absorb only certain specific amounts of energy. © 2014 Pearson Education, Inc. 4 3/10/2015 Energy states of the Bohr model • The energy of the atom is inversely proportional to the square of the quantum number n: © 2014 Pearson Education, Inc. Emission and absorption of photons © 2014 Pearson Education, Inc. 5 3/10/2015 How lasers work © 2014 Pearson Education, Inc. Lasers 6 3/10/2015 Summary of quantum numbers • Principal quantum number: • Orbital angular momentum quantum number: • Magnetic quantum number: • Spin magnetic quantum number: © 2014 Pearson Education, Inc. Emission Spectra Slide 29-30 7 3/10/2015 De Broglie waves and Bohr's third postulate • For an electron wave to be stable, an exact integer number n of electron wavelengths must be wrapped around the nucleus: • This is precisely Bohr's third postulate! © 2014 Pearson Education, Inc. Matter Waves An electron beam passing through a double slit produces an interference pattern similar to that for light. = = 1− 1− = = = = Slide 28-18 8 3/10/2015 The Particle in a Box 2 = 2 = = = = 2 2 The possible modes are reminiscent of those for the modes of a stretched string. The possible modes have different energies: Slide 28-19 Colors of Dyes The color of dyes results from the preferential absorption of certain wavelengths of light. For certain dyes, such as the cyanine dye of which a portion is illustrated below, we can determine the absorption wavelengths by using a simple particle in a box model. The dye molecules consist of symmetric pairs of rings joined at the center by a chain of carbon atoms. Electrons of the bonds along the chain of carbon atoms are shared among the atoms in the chain, but are repelled by the nitrogen-containing rings at the end of the chain. These electrons are thus free to move along the chain but not beyond its ends. They look very much like a particle in a onedimensional box. For the molecule below, the effective length of the “box” is 0.85 nm. What are the energies of the first five states?. Slide 28-20 9 3/10/2015 Energy Levels and Quantum Jumps For the dye molecule on the previous slide, what are the energy values for levels n=1, 2, 3, etc? What wavelength light corresponds to a transition between the energy levels n=4 and n=5? What is the maximum photon energy that could be emitted by the quantum system with the energy level diagram shown below? The minimum photon energy? A. 7.0 eV B. 6.0 eV C. 5.0 eV D. 4.0 eV E. 3.0 eV F. 2.0 eV G. 1.0 eV 10 3/10/2015 The uncertainty principle • A connection exists between the narrowness of the slit and the apparent y-component of the electron's momentum once it passes through: = = = = © 2014 Pearson Education, Inc. Uncertainty principle for energy • Because a fundamental limit exists on the determinability of the momentum of a particle, a fundamental limit should also exist on the determinability of the energy of the photon: © 2014 Pearson Education, Inc. 11