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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 l.jpg

Chapter 04Structure of the Atom

General Bibliography

1) Various wikipedia, as specified

2) Thornton-Rex, Modern Physics for Scientists & Eng, as indicated


Outline l.jpg
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 l.jpg
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 l.jpg
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 l.jpg
4.2 Geiger-Marsden-Rutherford

Assume massive positive objects

Coulomb force

Derivation on pages 131-137


4 2 geiger marsden rutherford6 l.jpg
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 l.jpg
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 model8 l.jpg
4.3 Classical Atomic Model

Failures of the classical model:

1.

2.


4 4 bohr s postulates l.jpg
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 5 successes failures of bohr model13 l.jpg
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+