Download - Waves, Light, Quantum
Waves, Light, Quantum
Figure 4.1: Molar Volume
(elements known in 1869)
0
10
20
30
40
50
60
70
80
0 50 100 150 200 250
relative atomic mass
Li
Na
K
Rb
Cs
Ge
Ga
Si
Sn
(a few more recently discovered elements added)
Other Periodic Trends
0
1000
2000
3000
4000
5000
6000
0 50 100 150 200 250
relative atomic mass
C
Li
NaK Rb Cs
Si
Sn
Pb
ClBr I
F
Ge
Ga
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View of White Light Through Spectroscope (Investigate This 4.5)
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white light viewed through slit
light separated into different wavelengthsby diffraction grating
white light source
white light source covered with permanganate solution
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KMnO4
View of White Light Source Through KMnO4 Solution (Investigate This 4.5)
Color of Wavelengths Absorbed is Complementary To Color Observed
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Purple Appearing Light
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Emission vs. Absorption(Consider This 4.7)
light source
white light source
some matter(light absorber)
prism (wavelength separator)
Light = Electromagnetic Waves
Electromagnetic radiation
the emission and transmission of energy
in the form of electromagnetic waves
one cycle
wavelength
amplitude
Properties of Waves
= wavelength = length of one cycle
frequency = number of cycles/time
Properties of Waves
c = velocity of light wave in vacuum
= 3.00 x 108 m/s
x c
= c/
= (3.00 x 108 m/s) / 4.69 x 1014 Hz
= 6.40 x 10-7 m
Problem 4: A laser used to weld detached retinas produces light with frequency of 4.69 x 1014 Hz. What is this wavelength in nm? To what part of the electromagnetic spectrum does this light belong? (1Hertz = 1 s-1.)
= 640 nm (red region of visible spectrum)
Waves In a Ripple Tank(Investigate This 4.12, 4.16)
Click on ripple tank wave simulation For 4.12
Set to Setup: Single Source; 1 Src, 1 Freq; Color Scheme 3
For 4.16 Change Setup to Double Slit (source
automatically switches to 1 Plane Src, 1 Freq)
Planck’s Quantum Theory
Planck’s Basic Ideas E states of a system (e.g., atom) are
quantized, not continuous
E
Classical Physics Viewcontinuous E states
state 3
state 2
state 1
Planck’s Quantum Viewquantized E states
Planck’s Basic Ideas Only certain E increments may be
absorbed or emitted by system
E
Classical Physics Viewcontinuous E states
infinite #of E possible
state 3
state 2
state 1
Planck’s Quantum Viewonly transitions allowed are between
quantized E states
emissions
Planck’s Basic Ideas Energy is emitted or absorbed in discrete units
(quanta)
E = hPlanck’s Law)
h = 6.63 x 10-34 J•s
E3˝1 = h
state 3
state 2
state 1
E
The Photoelectric Effect
Light strikes metal surface and ejects an electron
Classical physics predicts light intensity determines if e- is ejected.
But e- is ejected only if light of minimum is
used; intensity does not matter.
h e-
The Photoelectric Effect
Einstein: Quantum Theory Explains the PE Effect
Light is a stream of photons
Ephoton > Ee-
e- ejected withkinetic energy
e-
Ephoton < Ee- e- not ejected
Ee-
e- in metal
Ephoton = Ee- e- ejected
e-removed
Ephoton = h
What is ?(What is needed to eject e-?)
How much E must the e- absorb if it moves from n=1 to n=oo?
Ee- = Ee-,n=oo - Ee-,n=1
This increase in Ee- is supplied by the photon
Ee- = Ephoton = hor =Ee- /h E1 ˝ oo = h
oo
1
Ee-