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 4.5 Failures of the Bohr Model 4.6 Characteristic X-Ray Spectra 4.7 Atomic Excitations

with negative ‘raisins’ 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.

4.1 Geiger-Marsden-Rutherford 2. Radium alpha source, gold foil, ZnS screen, microscope. 3. Plum pudding model expect heavy alpha particles to plow through the pudding. If the alphas hit an electron, the deflection angles will be very small, R&T do a back-of-the-envelope calculation and get about 1deg of deviation with each collision. 4. Geiger & Marsden observed lots of particles bouncing to larger angles. 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

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

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

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

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

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

4.4 Bohr Model

4.4 Bohr Model

4.5 Successes & Failures of Bohr Model Reduced Mass Correction

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+

4.6 Characteristic X-Ray Spectra

4.7 Atomic Excitation