Technologies Associated with Electromagnetic Radiation

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Technologies Associated with Electromagnetic
Radiation

• VIS Radiation Color, Atomic Spectra

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A. Electromagnetic Spectrum
Tro, 162
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Visible Spectrum (VIS)
Each wavelength in the VIS region has a color and
a specific energy associated with it
Tro, 162
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B. Visible Radiation (VIS)

• 1. Interaction with Molecules
• 2. Applications
• a. Color
• b. Identifying elements

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Energy States of Atoms or Molecules

• Energy state of an atom or molecule refers to the
  arrangement of its electrons in orbits
  
• Ground state - all electrons are in lowest-energy
  orbits possible
  
• Excited state - all electrons are not in
  lowest-energy orbits possible
  

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How VIS Radiation Interacts with a Molecule
Tro, 164
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Fates of Excited Molecules
(a) Energy breaks bonds (b) and (c) -
return to ground state - no bonds broken

Tro, 164
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Color

• Color of an object depends on how its molecules
  interact with white light
  
• If molecules do not absorb any light, the
  reflected light is white, object is white
  
• If molecules absorb all light, there is no
  reflected light, object appears black
  
• If molecules absorb some light and reflect the
  rest, object appears colored
  

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Absorption and Reflection of Color
All colors reflected white
All colors absorbed black
Y, G and B reflected, rest absorbed green
Tro, 157
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Dye Technology

• Dyes are molecules that absorb VIS wavelengths
  and reflect specific colors
  
• Molecules can be synthesized so as to absorb
  specific wavelengths
  
• In general, the greater the number of alternating
  double bonds in a molecule, the longer the
  wavelength of light the molecule will absorb

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Reflectance and Absorption Spectra of a Molecule
B G Y reflected
Chemical Innovation, February 2000, 20
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Identifying an Element
Tro, 166
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Emission Spectra of H and He
Wavelengths in nanometers
Brescia et al, General Chemistry, 5th Saunders,
1988, 140g
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Technologies Associated with IR, Microwave

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F. Infrared Radiation (IR)
1. Interaction with molecules
2. Application
a. Identifying molecules
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Infrared Spectroscopy (IR)
IR excites vibratory motions of molecules
.
Ebbing, General Chemistry, 4th, Houghton
Mifflin,MA, 1993 ,363
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Each Molecule Has a Unique IR Spectrum
Certain groups of atoms, however, always absorb
at essentially constant wavenumbers (1/l in cm)
such as C-O(1200), CO(1750), and C-H(2950)
Ebbing, General Chemistry, 4th, Houghton
Mifflin,MA, 1993 ,364.
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G. Microwave radiation
1. Interaction with molecules
2. Application
a. Cooking food
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Interaction of Microwaves with Molecules

• Polar molecules absorb microwave radiation by
  exciting rotational motion
  
• Non-polar molecules are unaffected by microwave
  radiation allowing deep penetration of target
  matter
  
• Friction from rapidly rotating polar molecules
  produces heat
  

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Interaction of Polar Molecule with Microwaves
Chang, Chemistry, 6th, McGraw Hill, MA, 1998, 383
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In a microwave oven the fre-quency is 2.45 GHz
which is particularly suitable for increasing the
rotational energy of water molecules.
Magneton produces microwaves and rotating blades
disperse the radiation throughout the oven
Chang, Chemistry, 6th, McGraw Hill, MA, 1998, 38