Chapter 2, Lecture 1

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DEVELOPMENT OF ATOMIC MODELS
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Dalton First Atomic Theory
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J. J. Thomson
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Cathode Ray Tube
C
P
F
e-
Q
to vacuum pump
V
e- - cathode ray from filament F V - accelerating
voltage C - plate with hole to focus e- P Q -
charged plates of length l
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C
P
F
e-
Q
to vacuum pump
V
Figure 2.8
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Figure 2.9
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plum pudding model
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Cathode Ray Tube
Charge to Mass Ratio, Proceedure 1. reference
beam w/ no charge on plates PQ 2. apply charge of
known value (E) across PQ 3. measure deflection
(y) as beam passes thru l
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Cathode Ray Tube
eEl2 2mv2
e m
2yv2 El2

• y --gt
• -1.76 x 108 C/g

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Milikan Oil Drop ExperimentFigure 2.10
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density of oil 0.851 g/cm3
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Milikan Oil Drop Experiment

• Trial 1 rdrop 1.64 x 10 -4 cm
• E 1.92 x 105 N/coulwhere N unit of force
  F ma

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Milikan Oil Drop Experiment

• E 1.92 x 107 g/coul
• Vdrop ??r 3 1.85 x 10 -11 cm3
• E (.851 g/cm3) x (1.85 x 10 -11 cm3)
• x (1coul/1.92x107g)
• 8.0 x 10 -19 coul

4 3
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Trial E 1 8.0 x
10-19 C 2 3.1 x 10-19 C 3
6.5 x 10-19 C 4 9.5 x
10-19 C
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Trial E 1 5(1.6 x
10-19 C) 2 2(1.6 x 10-19 C) 3
4(1.6 x 10-19 C) 4 6(1.6 x 10-19
C)
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Rutherford Gold Foil Experiment
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Gold Foil ExperimentFigure 2.12
u
? - particles
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Pb block
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Gold Foil Experiment
u
? - particles
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Pb block
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Gold Foil Experiment

• Results
• 1. No holes
• 2. ?- particles deflected at specific
  angles - some backwards

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Gold Foil Experiment

• Rutherford (1911) Nuclear Model

heavy central() nucleus
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e- aboutnucleus
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The Bohr Model
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The Atom

• Dalton (early 1800s)

indivisible
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The Atom

• Thompson ( 1900)

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cloud of () charge
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electron(-) charge
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plum pudding model
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The Atom

• Rutherford ( 1911)

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heavy central() nucleus
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(e-) aboutnucleus
Nuclear Model
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The Atom
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• Bohr ( 1913)

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e- inallowed orbits
central ()nucleus
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Planetary Model
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The Atom

• Heisenberg, de Broglie, Schroedinger (mid 1920s)

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e- in regionsdefined by mathfunctions
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Quantum Mechanical Model