Electronic Structure of Atoms

1
Chapter 6

• Electronic Structure of Atoms

2
Light

• The study of light led to the development of the
  quantum mechanical model.
• Light is a kind of electromagnetic radiation.
• Electromagnetic radiation includes many kinds of
  waves
• All move at 3.00 x 108 m/s (c)

Speed of Light
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Parts of a wave
Origin
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Parts of Wave

• Origin - the base line of the energy.
• Crest - high point on a wave
• Trough - Low point on a wave
• Amplitude - distance from origin to crest
• Wavelength - distance from crest to crest
• Wavelength - is abbreviated l Greek letter lambda.

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Frequency

• The number of waves that pass a given point per
  second.
• Units are cycles/sec or hertz (hz)
• Abbreviated n the Greek letter nu
• c ln

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Frequency and wavelength

• Are inversely related
• As one goes up the other goes down.
• Different frequencies of light are different
  colors of light.
• There are a wide variety of frequencies
• The whole range is called a spectrum

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Sample Problem

• Calculate the frequency for yellow light with a
  wavelength of 589 nm.

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Quantized Energy and Photons

• Quanta fixed amount
• E h n
• E is the energy of the photon
• n is the frequency
• h is Plancks constant
• h 6.626 x 10 -34 Joules sec.
• joule is the metric unit of Energy

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Calculate

• What is the quanta of energy absorbed from yellow
  light (589 nm)?
• What is the energy per mole?

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Radiowaves
Microwaves
Infrared .
Ultra-violet
X-Rays
GammaRays
Long Wavelength
Short Wavelength
Visible Light
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The Photo Electric Effect

• When light is incident on certain metallic
  surfaces, electrons are emitted from the surface
• This is called the photoelectric effect
• The emitted electrons are called photoelectrons
• First discovered by Hertz
• Successfully explained by Einstein in 1905
• Received Nobel Prize in 1921 for paper on
  electromagnetic radiation, of which the
  photoelectric effect was a part

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The Photo Electric Effect
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Properties of light
The equation Ehv implies that photons of blue
light are more energetic than photons of red
light and that ultraviolet photons are more
energetic than photons of visible light.
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Photoelectric Effect Schematic

• When light strikes E, photoelectrons are emitted
• Electrons collected at C and passing through the
  ammeter are a current in the circuit
• C is maintained at a positive potential by the
  power supply

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Photoelectric Effect
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Application Photocells

• Photocells are an application of the
  photoelectric effect
• When light of sufficiently high frequency falls
  on the cell, a current is produced
• Examples
• Streetlights
• garage door openers
• Elevators
• Solar calculator