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-