Atomic Theory and Spectroscopy

1
Atomic Theory and Spectroscopy

• Clues to the Nature of Atoms

2
The Nature of Light and Radiation

• Electrons exist in discrete, unique energy
  levels.
• If exposed to energy which matches those levels,
  they leap to unstable higher energy levels.
• As they fall back they emit that energy at a
  wavelength and frequency which can be detected.

3
Electromagnetic Radiation

• Energy emitted by electrons can be detected at
  any part of the electromagnetic spectrum
• Ultraviolet light is emitted by many elements
• Many atoms emit energy at many different
  wavelengths at once
• Electromagnetic Spectrum
• Most elements emit visible radiation as different
  colors of light
• A spectroscope can view the unique, bright-line
  spectrum of light emitted by each element

4
Infrared Detection

• Pit vipers can detect heat emitted by animals .

5
Examples of nonvisible detection

• http//home.centurytel.net/Arkcite/uv.htm
• Ultraviolet photography
• http//www.youtube.com/watch?vkaPIh2XlaVMfeature
  related
• Infrared thermal photography

6
Measuring Electromagnetic Radiation

• Radiation can take many forms across the
  electromagnetic spectrum
• All radiation constantly travels through space at
  the same velocity (speed) 3.0 x 108 m/s
• The speed of electromagnetic radiation AKA
• The speed of light

7
Measuring radiation II

• Two properties can be measured
• Wavelength (l)
• The distance from the same point on successive
  waves (measured in meters)
• Frequency (?)
• The number of times a wave passes a fixed point
  per second, or the number of times it travels up
  or down per second
• Measured in cycles per second or hertz (Hz)

8
Measuring radiation III

• The relationship can be described mathematically
  as follows c?l
• Or inversely proportional
• If one knows the frequency or wavelength, the
  other can be calculated
• ? c/l
• l c/?

9
Examples

• What is the wavelength of a radio signal that is
  broadcast at 99.7MHz?
• If lc/?, then the wavelength of this signal is
  the constant (the velocity) divided by the
  frequency
• 3.0 x 108meters/second / 9.97 x 107Hz (1/second)
  
• 3.0 m

10
Example problem 2

• What is the frequency of a radar beam that has a
  wavelength of 4.52cm?
• If f c/l, then
• 3.0 x 108 meters/second / 4.52 x 10-2m
• 6.63 x 109 Hz
• What is this in MHz?
• 6.63 x 109 Hz / 1 x 106 Hz/MHz
• 6.63 x 103

11
Electromagnetic spectrum and Energy

• Energy and frequency are directly proportional
• The higher the energy, the higher the frequency
• Energy and wavelength are inversely proportional
• The higher the energy, the shorter the wavelength
• Planck discovered the energy of a wave or photon
  of light is constant (6.626x 10-34J/Hz)
• Plancks constant (h)

12
Energy and Radiation II

• If one knows the frequency of a wave, then the
  energy of the wave can be calculated as well in
  the same manner
• Eh ?,
• Sample What is the energy of a wave which has a
  frequency of 103.5MHz?
• E 6.626 x 10-34J/Hz x 1.035 x 108 Hz
• 6.86 x 10-26J