Announcements
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◦ Access code is back-ordered
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◦ If you like to annotate on tablets, or can use for studying before exams
- Office hours, today, 1 – 2:30 pm, SCI 284
- Alchemist Session, Thurs., 7 - 9 pm, SCI 128
- Review Sessions for Primer to Chem 10: Friday 2 – 3:30 pm, SCI 183
Assignments
- P. Set 1 and OWL HW 1- due Wed., 9/8 at noon
Today
- Electromagnetic radiation (6.1)
- Energy Quantization (6.2)
Chapter 6:
Structure of Atoms
Sections 6.1-6.2
Electromagnetic radiation
1864, James Maxwell
◦ light and radiation = oscillating, wave-like electric and magnetic fields
◦ Visible light, microwaves, x-rays, etc = Electromagnetic radiation EMR
like
behavior and travels through space
the speed of
at
light in
radiant
1
É
the
wave
position
exhibits
wave
vacuum
I
f
energy that
Wavelength (λ, units = m):
distance between a given point on
a wave and the corresponding
point in the next cycle of the wave
Frequency (ν units = s-1s, Hz): the
number of waves (oscillations)
that pass a given point in some
unit of time (usually seconds)
Speed of light
speed
of
light
X
vacuum
in
C
M
C
X
t
2 998
108M
x
x
s
z
Electromagnetic spectrum
Decrease frequency, increase wavelength, and vice versa
Xx
Xv
m
a
Problem 1
An FM radio station broadcasts at 99.5 MHz. Calculate the
wavelength of the corresponding radio waves.
N
99.5
V
99.5
C
2.998
MHZ
106
106 HE
Hz
D
XXV
108
M
S
X
X
3.070
7
99.8 106 St
Radiation discoveries
Pre-1900, Classical Physics
◦ Thought matter and energy
were distinct
F
consists of
particles
has mass
pecified
E
E
light
a
is
wave
massless
young
experimental
cassical theory
1
p
◦ Thought matter can absorb
or emit any quantity of
energy
energy iscontinuous
match
didn't
theory
experimental observations
in ur
or catastrophe
region
Muy
Quantization of energy
1900, Max Planck
◦ Accounted for observed profiles by postulating that energy is quantized
◦ Quantization: emitted energy can only have certain energies
hut
integer
frequency
constant
◦ Discrete units, or “packets” of energy = quanta
change
leg
energy
it's heated
in
as
Ann
DE
it
al
between
change
adjacent E levels
of
system
a
e
f
Joules
n
w
Planks
constant3
6 626
10
5
Problem 2
The blue color in fireworks is often achieved by heating copper(I)
chloride (CuCl) to about 1200 degrees Celsius. The hot compound
emits blue light at a wavelength of 450 nm. What is the energy
emitted by CuCl?
T 12000C
c
XXV
950 nm
9
2
2.998 108 Mls
450 10 M XV
159
6.66 X 10M s
V
E
E
W
6.626
10
34
J's
x
6.66 101454
104950
5
4.4
450
E
C
V
E
X
V
her
M
Photoelectric effect
1905, Albert Einstein –
photoelectric effect
◦ Bombarded a piece of metal with
light
◦ Electrons emitted only when
frequency of light was greater than
or equal to threshold frequency
→Proposed that electromagnetic
radiation is quantized
→EMR can be viewed as a stream of
particles called photons
A EMR
has
ooo
ooo
particledality
wave
light
light
Ephoton
as
as
wave
a
a
Net
Maxwell
Planck
stream
of photons
Einstein