Light, Photon Energies, and Atomic Spectra

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Light, Photon Energies, and Atomic Spectra
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Electrons and Waves

• Louis deBroglie proposed the dual nature of
  matter, which means that matter has matter-like
  properties and wave-like properties.
• What are wave-like properties?
• Wavelength
• Frequency
• Energy

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Wave PropertiesWavelength

• Wavelength (?) is the distance from two
  consecutives higher or lower points of a wave
  (measured in meters m or nm)

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Wave PropertiesFrequency

• Frequency (?) is the number of times a wave
  completes a cycle in one second (cycles per
  second is Hertz or Hz or 1/ s or s-1)

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Light is Electromagnetic Radiation

• Electromagnetic energy is energy that has
  electric and magnetic fields
• There are many types of Electromagnetic
  Radiationvisible is just one type!

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Electromagnetic Spectrum
Longer Wavelength (l) Smaller Frequencies
(n) Less Energy (E)
Shorter Wavelength (l) Larger Frequencies
(n) Higher Energy (E)
Roy G. Biv
Longer Wavelength (l) Smaller Frequencies
(n) Less Energy (E)
Shorter Wavelength (l) Larger Frequencies
(n) Higher Energy (E)
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Quick Check Electromagnetic Spectrum

1. Which type of wave in the electromagnetic
   spectrum has the greatest energy?
2. Which type of wave has the longest wavelength?
3. List the waves of the visible spectrum in order
   of increasing energy.

Gamma Rays
Radio Waves
(Lowest ? Highest)
Red, Orange, Yellow, Green, Blue, Violet
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Relationship between Wavelength and Frequency

• As the wavelength increases, the frequency of the
  wave decreases.

• Important Note(s)
• Wavelength must be in meters.
• Frequency must be in Hertz.

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Example 1
f

• A purple light has a frequency of 7.42 x 1014
  s-1.  What is its wavelength?

c f l
3.00 x 108 m/s
(7.42 x 1014 s-1)
l
7.42 x 1014 s-1
7.42 x 1014 s-1
l 4.04 x 10-7 m
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Example 2

• Certain elements emit light of a specific
  wavelength when they are burned. For example,
  silver emits light with a wavelength of 3.18 x
  10-7 m. Determine the frequency of the wave
  emitted by silver.

c f l
(3.18 x 10-7 m)
f
3.00 x 108 m/s
3.18 x 10-7 m
3.18 x 10-7 m
f 9.43 x 1014 s-1 or Hz
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Example 3 Now You Try!

• The yellow light given off by a sodium vapor lamp
  used for public lighting has a frequency of 5.09
  x 1014 Hz. What is the wavelength of this
  radiation?

c f l
3.00 x 108 m/s (5.09 x 1014 Hz) l
l 5.89 x 10-7 m
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Relationship between Frequency and Energy

• As frequency increases, the energy of the wave
  increases.

• Important Note
• Frequency must be in Hertz.

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Example 4

• What is the energy of a photon if it has a
  frequency of 6.82 x 1017 Hz?

f
E hf
E
(6.63 x 10-34 Js)
(6.82 x 1017 Hz)
E
4.52 x 10-16 J
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Example 5 Now You Try!

• Determine the frequency of a wave that has a
  energy of 8.72 x 10-18 J.

E
E hf
(6.63 x 10-34 Js) f
8.72 x 10-18 J
f 1.32 x 1016 Hz
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Putting the Two Together

• Example 6
• What is the energy of a photon of blue light that
  has a wavelength of 4.5 x 10-7m?

(6.63 x 10-34 Js)
(3.00 x 108 m/s)
E
4.4 x 10-19 J
4.5 x 10-7m
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Atomic Spectrum

• How color tells us about atoms
• Atomic Emissions

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Energy in Atoms
A Closer Look at the Spectra and Bohrs Model of
the Atom
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What does this have to do with electron
arrangement in atoms?

• When all electrons are in the lowest possible
  energy levels, an atom is said to be in its
  GROUND STATE.
• When an atom absorbs energy so that its electrons
  are boosted to higher energy levels, the atom
  is said to be in an EXCITED STATE.

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Atomic Spectrum

• Each element gives off its own characteristic
  colors.
• Can be used to identify the atom.
• That is how we know what stars are made of.
• Bright Line Emission Spectra
• Energy Levels and Spectra movie

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• These are called line spectra
• unique to each element.
• These are emission spectra