Evolution of models of atomic structure

1
Evolution of models of atomic structure
Breakdown of classical physics

• Atoms atomo? (Greek) indivisible
• first speculative atomistic theories by
• Demokritus Plato Aristoteles
• (460 370 BC) (429 348 BC) (384 322
  BC)

lt pictures from www.wikipedia.org gt
2
... more than 2000 years later ...

• Law of definite proportions (1794) by
• Joseph Louis Proust
• (1754 1826)
• First table of atomic weights (1803) by
• John Dalton
• (1766 1844)

lt pictures from www.wikipedia.org gt
3
... more than 2000 years later ...

• 1833 atomic properties of electricity in
• electrolysis found by Michael Faraday
• (1791-1861)

lt picture from www.wikipedia.org gt
4
How indivisible are atoms?

• Joseph John Thompson (1865 1940)
• works with cathode rays
• 1897 he discovers that the charged particles in
• cathode rays have negative charge. He
• measures their charge-to mass ratio and
• identifies them as electrons postulated 1874
• by G. Johnston Stoney as units of charge.

-
10 kV
lt picture from www.wikipedia.org gt
5
1909 Robert A. Millikan (1868 1953) measures
the magnitude of the elementary charge
Nobel Prize 1923
lt picture from www.wikipedia.org gt
6
Thompsons Plum Pudding Model
raisins
pudding
electrons are discrete particles embedded in a
smeared out positive background charge
lt picture from www.wikipedia.org gt
7
Rutherfords Experiment
Scattering Intensity (arb. units)
random walk (Thompson model)
?
Rutherford model
from Gerthsen, Kneser, Vogel Physik
8
Emission Spectra
Emission spectrum of Hydrogen
Emission spectrum of Iron
9
1913 Bohrs Model of the Atom
Niels Hendrik David Bohr 1885 - 1962
Nobel Prize for Physics, 1922
lt pictures from www.wikipedia.org gt
10
Matter Waves
Louis Victor Pierre Raymond, 7e Duke of
Broglie (1892 - 1987)
Nobel Prize for Physics, 1922
lt picture from www.wikipedia.org gt
11
Superimpose 2 waves with different momenta
12
Superimpose 10 waves with different momenta