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Chemistry 1B-01, Fall 2013 Lectures 1-2
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Chemistry 1B
Fall 2013
lectures 1-2(ch 12 pp 522-536)6th
[ch 12 pp 522-537]7th
30 Nature of light and matter. Wave-particle duality chap.12 p524-531
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• Why? To understand the behavior of electronsin atoms an molecules
goals of lectures 1-2
• The “laws of nature” in 1900 (successful for describing large objects)
describe particles AND describe waves
• Experiments that contradicted these laws(when applied on the scale of atomic dimensions)
Ultraviolet Catastrophe and Photoelectric Effect Spectrum of Hydrogen Atom Davisson-Germer and Compton Experiments
• particles BEHAVE AS waves
waves BEHAVE AS particles
• obtain and use observed quantitative relationships (HW #1)
• Why? To understand the behavior of electronsin atoms an molecules
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physics and chemistry in 1900
• fundamental particles and chargeelectron: - charge, me= 9.109 10-31 kgproton: + charge, mp= 1.672 10-27 kgneutron: 0 charge, mn= 1.675 10-27 kg
[Table 2.2 and back cover]
• particles in general
• electromagnetic waves
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light waves
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properties of electromagnetic radiation (light WAVES)
• electromagnetic wavefig 12.1~fig 12.2 (amplitude, wavlength, frequency)
fig 12.3 (electromagnetic spectrum)
spectrum of visible light
• wave phenomena (properties of ‘classical’ waves)
• dispersion [in a material light (EM waves) of differing frequencieswill have differing velocities , different ‘refractive indices’]
• refraction [bending of light (EM wave) when passing between materials of differing ‘refractive index’]
• diffraction [EM waves bend when confined by a slit; diffraction pattern]
• interference [waves can interact constructively (add; reinforce) and destructively (subtract, cancel)]
and Fig. 12.7 interference pattern]
DO
N’T
FR
ET
HW#1 PROB 12.1F2013
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Planck’s Formula
• Blackbody radiation- Fig 12.4
• Ultraviolet catastrophe (p. 525)
• E=h (energy per photon)
(HW#1 PROB 12.21F2013, 12.124 F2013)
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Chemistry 1B-01, Fall 2013 Lectures 1-2
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some comments about “energy” ( sec 9.1, pp. 359-360)
• kinetic energy (HW #5.77F2013 ; see p 168
KEAVG= (3/2)RT (per mole)
KEAVG= (3/2)kT (per molecule)
• potential energy
• conservation of energy
• momentum (p. 158)
• units and conversions
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photoelectric effect (pp 514-515)
• apparatus Sil Fig. 7.7
• what’s observed
• interpretation (HW#1 12.27 F2013)
photoemissive
material
anode collector
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−
photoelectric effect : electron in a “potential well” (CLASSICAL: small amplitude, long wavelength)
ener
gy
low amplitudewave
(long l)
no electron ejected
attraction of metal
for election
is work function (value depends on the metal being irradiated)
example for potassium=3.68x10-19J= 2.29eV
low amplitudewave
(long l)
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−
photoelectric effect : electron in a “potential well” (CLASSICAL: large amplitude, long wavelength)
ener
gy
nada: no electron ejected (RED IS JUST A LOSER WAVELENGTH)
attraction of metal
for election
large amplitudewave
(long l)
CLASSICALLY:just increase amplitude to get enough energy to eject electron !!
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−
photoelectric effect : electron in a “potential well” (= long)
ener
gy
low energyphoton
no electron ejected
attraction of metal
for election
example for potassium =3.59x10-19J= 2.24eV
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−
photoelectric effect : electron in a “potential well” ( = medium)
ener
gy medium energyphoton
no extra energy for KE
attraction of metal
for election
example: for potassium (depth of ‘potential well’) = 3.59x10-19J = 2.24eV
photon of this energy: E=hn=hc/l l=(c/n)=(ch/E)=553 nm
(l=553nm color?)
3.59x10-19J
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Chemistry 1B-01, Fall 2013 Lectures 1-2
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−
photoelectric effect : electron in a “potential well” ( = short)
ener
gy high energyphoton
mucho extra energy for KE
attraction of metal
for election
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summary of observations
KE
of
ejec
ted
ele
ctro
ns
frequency of light ( )
cesium sodium
0=Cs
h0= Na
h
for given > 0 increase intensity of light more photons, but E per photon remains same more electrons, but of same kinetic energy
0= 4.60 1014 sec-1
l0= 652.6 10-9 m = 652.6 nm
0= 5.95 1014 sec-1
l0= 504 10-9 m = 504 nm
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conservation of energy (p 527)
if a individual photon that has sufficient energy to ‘kick’ electron out of the potential well of metal:
if an individual photon does not have sufficient energyto ‘kick’ electron out of the potential well of metal:
NO ELECTRONS EJECTED !!
energy of photon= energy to get out of well + kinetic energy of electron
(HW#1 12.27 F2013,12.29 F2013)
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• classical prediction (death spiral)
• observation of atomic spectra fig. 12.8
• Bohr model (HW#12012 12.35a,d, 12.36, *12.39)
fig. 12.10, Silberberg 7.10
spectrum of atomic hydrogen
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Davisson-Germer experiment (shoot electrons at crystal (foil)??)
X-ray diffractionof Al foil
Electron diffractionof Al foil
mind blowing
diffraction by slits and crystals
constructive int
destructive int
remember: WAVES showed
x-rays electrons ??
constructive int
destructive int
constructive and destructive interference
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wave-particle duality
• diffraction of electrons-(Davisson-Germer Experiment; p. 530)
• De Broglie relationship (p. 528) (HW#12012 12.30,12.33)
• What is “meaning” of electron wave?? (http://phys.educ.ksu.edu/vqm/html/doubleslit/index.html)(http://www.youtube.com/watch?v=DfPeprQ7oGc)
• Wavelengths of “ordinary” objects (p. 528, example 12.2) Silberberg Table 7.1 (HW#12012 prob S2)
• Compton Experiment
• Heisenberg uncertainty principle (p. 539) boing!! (HW#12012 12.45)
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Chemistry 1B-01, Fall 2013 Lectures 1-2
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goals of lectures 1-2
• The “laws of nature” in 1900 (successful for describing large objects)
describe particles AND describe waves
• Experiments that contradicted these laws(when applied on the scale of atomic dimensions)
Davisson-Germer and Compton Experiments
Ultraviolet Catastrophe and Photoelectric Effect
Spectrum of Hydrogen Atom
• particles BEHAVE AS waves
waves BEHAVE AS particles
• Ensuing quantitative relationships
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What to do ??
invent quantum mechanics !!!
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Solvay Conference 1927
The mid-1920's saw the development of the quantum theory, which had a profound effect on chemistry. Many theories in science are first presented at international meetings. This photograph of well-known scientists was taken at the international Solvay Conference in 1927. Among those present are many whose names are still known today. Front row, left to right: I. Langmuir, M. Planck, M. Curie, H. A. Lorentz, A. Einstein, P. Langevin, C. E. Guye, C. T. R. Wilson, O. W. Richardson. Second row, left to right: P. Debye, M. Knudsen, W. L. Bragg, H. A.Kramers, P. A. M. Dirac, A. H. Compton, L. V. de Broglie, M. Born, N. Bohr. Standing, left to right: A. Piccard, E. Henriot, P. Ehrenfest, E. Herzen, T. De Donder, E. Schroedinger, E. Verschaffelt, W. Pauli, W. Heisenberg, R. H. Fowler, L. Brillouin.
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‘fuel’ for quantum mechanicians
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quantum mechanics: WEIRD
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end of lectures 1-2
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Chemistry 1B-01, Fall 2013 Lectures 1-2
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figure 12.1 Zumdahl
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figure ~12.2
=c
HW PROBS #12.22 F2013, 12.28
wave amplitude
wavelength (l) and frequency (n )
c=speed of light2.996 â 108 m s-1
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Silberberg figure 7.2
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Zumdahl figure 12.3
HW PROBS #12.21F2013, #12.26
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R O Y G B I V
ROY G BIV
wavelength and color
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Silberberg figure 7.5 and Zumdahl 12.7
constructive=high intensity
destructive=low intensity
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Chemistry 1B-01, Fall 2013 Lectures 1-2
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Zumdahl figure 12.3 and Silberberg figure 7.6
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Ultraviolet catastrophe
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Silberberg figure 7.7
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classical “decay and death of hydrogen atom”
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Zumdahl figure 12.8
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Silberberg figure 7.10 (emission: H-electron loses energy)
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Chemistry 1B-01, Fall 2013 Lectures 1-2
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Silberberg figure 7.10 (absorption, H-electron gains energy)
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Zumdahl figure 12.10
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Silberberg figure 7.5 and Zumdahl 12.7
constructive=high intensity
destructive=low intensity
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from http://phys.educ.ksu.edu/vqm/html/doubleslit/index.html
photons l= 402 nm
electrons v=3.06 106 m sec-1photons l= 594 nm
[slit 10-5 m] [slit 5 10-9 m]
electrons v= 4.6 106 m sec-1
l increases x 1.5 v decreases x 1.5l increases
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Silberberg Table 7.1
note mass in g, need to use kg for mvl=h(l correct in table)
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wavelike properties of C60 (fullerene)
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Chemistry 1B-01, Fall 2013 Lectures 1-2
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waves: x vs v
xx
y
Vx Vx
x larger x smaller
vx smaller vx larger49
Uncertainty and measurement
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particles in classical physics
• particles have mass (m) , definite positions (x) and velocities (v)
• particles have kinetic energyand momentum p=mv
• particles obey Newton’s laws of physics F=ma
HW#1 PROB 12.1F2013