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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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Chapter 04Structure 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


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

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


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