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Transcript of Ch 28 Powerpoint_1
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Chapter 28
Atomic Physics
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Emission Spectrum of Hydrogen
Experimentally, the wavelengths of hydrogens
spectral lines are described by series such as the
Balmer series:
RH is the Rydberg constant RH = 1.0973732 x 10
7 m-1
n is an integer, n = 1, 2, 3,
!
P 22H
n
1
2
1R
1
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Spectral Lines of Hydrogen
Examples of BalmerSeries spectral lines
n = 3, = 656.3 nm
n = 4, = 486.1 nm
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Examples of Emission
Spectra
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Hg Spectrum Demo
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Bohrs Model for Hydrogen
2
21
2e e
eE KE PE m v k
r! !
2
2
ek eEr
!
And if the force of attraction
provides the centripetal
acceleration, then:
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Bohrs Model for Hydrogen cont.
Then Bohr assumed that the electrons orbitalangular momentum is quantized!
mevrn = nh/2T
with n = 1, 2, 3, The principle quantum number
resulting in only certain orbits allowed.
(h = Plancks constant = 6.626 x 10-34 Js)
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Bohrs Model for Hydrogen cont.
With the result that the
energy of the allowed
orbits are:
En = - 13.6 eV/ n2
rn = n2 a0
with a0=0.0529 nm
The Bohr Radius
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Bohrs Energy Level Diagram
Predictions inexcellent
agreement withexperimental data
for Hydrogen
including for RH.
!
P 22H
n
1
2
1R
1
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Photon Energy
Whenever a transition occurs
between a state, ni to another state,
nf(where ni > nf), a photon is emitted.
The photon has a frequency
f = (Ei Ef)/h and wavelength
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Active Figure 28.6
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Active Figure 28.17
An Ionization Problem
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Characteristic X-Rays
When a metal target isbombarded by high-energy electrons, x-raysare emitted.
The x-ray spectrumtypically consists of abroad continuousspectrum and a series ofsharp lines.
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Wave Mechanics - de Broglie Waves
To quantize angular
momentum, de
Broglie then assumedthat an electron orbit
must contain an
integral number of
electron wavelengths.
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de Broglie Waves cont.
De Broglies approach:
resulted in the same quantization ofangular momentum as Bohr used.
indicated that the wave nature of matterwas central to modeling the behavior ofatomic systems.
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Quantum (wave) mechanics
Better experiments and quantum mechanics have
both led to more quantum numbers:
n the principle quantum number (K, L M .
lthe orbital quantum number (s, p, d, f..
mlthe orbital magnetic quantum number
ms the spin magnetic quantum number
All with rules!
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But, The Pauli Exclusion Principle
states that:
No two electrons in an atom can ever have
the same set of values of the quantum
numbers n, , m , and ms.
That explains the electronic structure of
complex atoms as a succession of filled
energy levels with different quantum
numbers.
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Atomic configuration question