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Welcome to 3.091
Lecture 3
September 14, 2009
Atomic Models: Rutherford & Bohr
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Periodic Table Quiz
Name Grade /10
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La Lazy
Ce college
Pr professorsNd never
Pm produce
Sm sufficiently
Eu educatedGd graduates
Tb to
Dy dramatically
Ho help
Er executives
Tm trim
Yb yearly
Lu losses. source unknown. All rights reserved. This image is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.
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La Loony
Ce chemistry
Pr professorNd needs
Pm partner:
Sm seeking
Eu educatedGd graduate
Tb to
Dy develop
Ho hazardous
Er experiments
Tm testing
Yb young
Lu lab assistants.
cannot be referring
to 3.091!
must be the other
chemistry professor
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CEase not I to slave, back breaking to tend;PRideless and bootless stoking hearth and fire.
No Dream of mine own precious time to spend
Pour'ed More to sate your glutt'nous desire.
SMelting anew my ten-thousandth hour
EUtopia forever I eschew.Growing Dimmer is my fleeing power
To Bid these curs'ed problem sets adieu.
DYing away whilst thy hosts are fought
HOpeless I come should in lecture I doze.
ERgo, like a sad slave, stay and rest nought.
Then Must I tool and toil while fatigue grows.Yet, Bloody though I must be, and quite ill
Light the Universal abyss I will.
57
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Lanthanum
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La3*
Courtesy of MIT Student. Used with permission.
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The Structure of the Atom
status report ca. end of the 19th century
* atom is electrically neutral
* -ve charge carried by electrons
* e- has very small mass
bulk of the atom is +ve,
most mass resides in +ve charge
Question:
what is the spatial distribution of charge inside an atom?
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Figure 1.18
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Figure 1.19
Paper0.5- cm lead10-cm lead
rays
particles
particles
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Rutherford-Geiger-Marsden experiment
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b
Marsden's Analysis
Scattering of an -particle which approaches a heavy nucleus with an impact parameter b.
qTrajectory of incident
particle
gold nucleus
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principles of modern chemistry:
* recognize patterns
* develop a quantitative model that
- explains our observations
- makes predictions that can betested by experiment
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Bohr Postulates for the Hydrogen Atom
1. Rutherford atom is correct2. Classical EM theory not applicable to orbiting e-
3. Newtonian mechanics applicable to orbiting e-
4. Eelectron = Ekinetic + Epotential
5. e- energy quantized through its angular momentum:
L = mvr = nh/2, n = 1, 2, 3,
6. Planck-Einstein relation applies to e- transitions:
E = Ef- Ei = h = hc/
c =
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Bohr Postulates for the Hydrogen Atom
1. Rutherford atom is correct2. Classical EM theory not applicable to orbiting e-
3. Newtonian mechanics applicable to orbiting e-
4. Eelectron = Ekinetic + Epotential
5. e- energy quantized through its angular momentum:
L = mvr = nh/2, n = 1, 2, 3,
6. Planck-Einstein relation applies to e- transitions:
E = Ef- Ei = h = hc/
c =
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Bohr Postulates for the Hydrogen Atom
1. Rutherford atom is correct2. Classical EM theory not applicable to orbiting e-
3. Newtonian mechanics applicable to orbiting e-
4. Eelectron = Ekinetic + Epotential
5. e- energy quantized through its angular momentum:
L = mvr = nh/2, n = 1, 2, 3,
6. Planck-Einstein relation applies to e- transitions:
E = Ef- Ei = h = hc/
c =
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Bohr Postulates for the Hydrogen Atom
1. Rutherford atom is correct2. Classical EM theory not applicable to orbiting e-
3. Newtonian mechanics applicable to orbiting e-
4. Eelectron = Ekinetic + Epotential
5. e- energy quantized through its angular momentum:
L = mvr = nh/2, n = 1, 2, 3,
6. Planck-Einstein relation applies to e- transitions:
E = Ef- Ei = h = hc/
c =
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0 500 1000 1500 2000 2500 3000
5000 K
4000 K
3000 K
Radiationintensity
Wavelength (nm)
Classical prediction6000 K
E = h
Planck suggests that light is composed of energy
packets or quanta. The elementary unit of e-m
radiation is thephoton.
InfraredVisibleUV
6000 K
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Bohr Postulates for the Hydrogen Atom
1. Rutherford atom is correct2. Classical EM theory not applicable to orbiting e-
3. Newtonian mechanics applicable to orbiting e-
4. Eelectron = Ekinetic + Epotential
5. e- energy quantized through its angular momentum:
L = mvr = nh/2, n = 1, 2, 3,
6. Planck-Einstein relation applies to e- transitions:
E = Ef- Ei = h = hc/
c =
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source unknown. All rights reserved. This image is excluded from ourCreative Commons license. For more information, see http://ocw.mit.edu/fairuse.
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Isotopes of Hydrogen
hydrogen1766 Henry Cavendish, London
deuterium
1931 Harold Urey, Columbia U.
tritium
1934 Ernest Rutherford, Cambridge U.
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Dalton proposes the
indivisible unit of an
element is the atom.
1803
Thomson discovers electrons,
believed to reside within a
sphere of uniform positive
charge (the "plum pudding"
model).
1904
Rutherford demonstrates the
existence of a positively charged
nucleus that contains nearly all
the mass of an atom.
1911
Bohr proposes fixed circular
orbits around the nucleus
for electrons.
1913
In the current model of the
atom, electrons occupy regions
of space (orbitals) around the
nucleus determined by their energies.
1926
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J. J. Thomson (1856-1940)
Cathode ray = Charged particle = Electron (1897)
charge-to-mass ratio of electron (1897)
J.J Thomson
"Plum pudding" model of
atom (1904)
Robert Millikan (1868-1953)
Charge and mass of electron
(1909)
James Chadwick
(1891-1974)
Neutron (1932)
Ernest Rutherford
Proton (1920)
Ernest Rutherford
Nuclear model of atom (1911)
Ernest Rutherford
(1871-1937)
and particles (1898)
Marie and Pierre Curie
(1867-1934, 1854-1906)
Radioactive elements
polonium and radium (1898)
Henri Becquerel (1852-1908)
Uranium emits rays that fog
photographic film (1869)
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3.091SC Introduction to Solid State ChemistryFall 2009
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