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Chapter 04 Structure of the Atom

Chapter 04 Structure of the Atom. General Bibliography 1) Various wikipedia, as specified 2) Thornton-Rex, Modern Physics for Scientists & Eng, as indicated. Outline. 4.1 Atomic Models of Thomson & Rutherford 4.2 Rutherford Scattering 4.3 Classical Atomic Model 4.4 Bohr Model

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Chapter 04 Structure of the Atom

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  1. Chapter 04Structure of the Atom General Bibliography 1) Various wikipedia, as specified 2) Thornton-Rex, Modern Physics for Scientists & Eng, as indicated

  2. Outline • 4.1 Atomic Models of Thomson & Rutherford • 4.2 Rutherford Scattering • 4.3 Classical Atomic Model • 4.4 Bohr Model • 4.5 Failures of the Bohr Model • 4.6 Characteristic X-Ray Spectra • 4.7 Atomic Excitations

  3. 4.1 Plum Pudding Model J.J. Thomson Positive pudding with negative ‘raisins’ Electrons oscillate about their equilibrium position when heated and produce EM radiation If made oscillations about ~10-10 m, could produce visible wavelengths, but never line spectra.

  4. 4.1 Geiger-Marsden-Rutherford http://en.wikipedia.org/wiki/Geiger%E2%80%93Marsden_experiment http://www.kutl.kyushu-u.ac.jp/seminar/MicroWorld1_E/Part2_E/P23_E/Geiger_Marsden_E.jpg

  5. 4.2 Geiger-Marsden-Rutherford Assume massive positive objects Coulomb force Derivation on pages 131-137

  6. 4.2 Geiger-Marsden-Rutherford Example 4.4 & 4.5: Estimate distance of closest approach for an alpha particle striking an aluminum nucleus KE = 7.7 MeV s

  7. 4.3 Classical Atomic Model v r Using Newtonian Mechanics & JJThomson’s anticipated sizes: 1. Estimate the speed of the orbiting electron 2. Total Energy of the system

  8. 4.3 Classical Atomic Model Failures of the classical model: 1. 2.

  9. 4.4 Bohr’s Postulates • A countable number of “stationary states” exist. (electrons in a selection of allowed orbit radii) • EM radiation emitted when electron jumps/transitions between states • Classical rules apply to stationary states, but not during transitions between states. • …Angular momentum occurs in integer multiples of h/2p. n=1 n=2 n=3

  10. 4.4 Bohr Model

  11. 4.4 Bohr Model

  12. 4.5 Successes & Failures of Bohr Model Reduced Mass Correction

  13. 4.5 Successes & Failures of Bohr Model • + Rydberg Eqn predicts many lines of He (except for a few extra lines) • Higher resolution diffraction gratings in advanced spectrographs indicated some transitions were multiple (fine structure) • Bohr’s “n” quantum number is only partially associated with angular momentum (1s, 2s, 3s,… states do not have angular momentum) • Worked best for single-electron atoms • H+, He+, Li+

  14. 4.6 Characteristic X-Ray Spectra

  15. 4.7 Atomic Excitation

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