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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