Transcript Slide 1

The Electronic Structure of Atoms
Ch. 7
Properties of Waves
Wavelength (λ) is the distance between identical points
on successive waves.
Amplitude is the vertical distance from the midline of
a wave to the peak or trough.
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Properties of Waves
Frequency (v) is the number of waves that pass through a
particular point in 1 second (Hz = 1 cycle/s).
The speed (u) of the wave = λ x ν
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Maxwell (1873), proposed that visible light consists
of electromagnetic waves.
Electromagnetic
radiation is the emission
and transmission of
energy in the form of
electromagnetic waves.
Speed of light (c) in vacuum = 3.00 x 108 m/s
All electromagnetic radiation
λxν=c
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Example 7.1
The wavelength of green light from a
traffic signal is centered at 522 nm.
What is the frequency of this
radiation?
Remembering that 3x108 m/s = 3x1017 nm/s will make your life easier!
5.75 x 1014 s-1
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A photon has a frequency of 6.0 x 104 Hz. Convert
this frequency into wavelength (nm). Does this
frequency fall in the visible region?
l
lxn=c
l = c/n
l = 3.00 x 108 m/s / 6.0 x 104 Hz
l = 5.0 x 103 m
l = 5.0 x 1012 nm
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n
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Energy (light) is emitted or absorbed in
discrete units (quantum).
E=hxn
Planck’s constant (h)
h = 6.63 x 10-34 J•s
Light has both:
1. wave nature
2. particle nature
Photon is a “particle” of light
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When copper is bombarded with high-energy
photons, X rays are emitted. Calculate the energy (in
joules) associated with the photons if the wavelength
of the X rays is 0.154 nm.
E=hxn
E=hxc/l
E = 6.63 x 10-34 (J•s) x 3.00 x 10 8 (m/s) / 0.154 x 10-9 (m)
E = 1.29 x 10 -15 J
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Line Emission Spectrum of Hydrogen Atoms
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Electrocution of a pickle
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…and fireworks
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lithium
sodium
potassium
SALT
COLOR OF FLAME
Sodium Chloride (NaCl)
Copper (II) Chloride (CuCl 2)
Lithium Chloride (LiCl)
Calcium Chloride (CaCl2)
yellow / orange
green
fuschia
orange
2
Strontium Chloride (SrCl2)
Barium Chloride (BaCl2)
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red
yellow / green
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Bohr’s model of the atom (1913)
1. e- can only have specific
(quantized) energy
values
2. light is emitted as emoves from one energy
level to a lower energy
level
En = -RH (
1
n2
)
n (principal quantum number) = 1,2,3,…
RH (Rydberg constant) = 2.18 x 10-18J
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E = hn
E = hn
Stopped here
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