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Section 4.7—Light & Matter
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Photon coming into atom collides with electron. Photons are energy.
Electrons Absorbing Energy
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Photon coming into atom collides with electron. Photons are energy.
Electrons Absorbing Energy
The electron is “excited” to a higher energy level with is newly increased energy from absorbing the photon.
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Excitation
The process of an electron absorbing a photon of light (energy) and being promoted to a higher energy level from its “ground state”
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The electron cannot remain in that excited state indefinitely
And later…
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The electron cannot remain in that excited state indefinitely
Energy is released during relaxation
And later…
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Relaxation
The process of an electron releasing a photon of light (energy) and falling back down to a lower energy level.
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Energy of photon and levels jumped
The higher the energy of the photon, the greater the electron jump!
A photon of UV light has more energy than a photon of Infrared light The UV photon would cause a higher energy
jump (jump up more levels) than the IR photon.
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Total energy in = Total energy out
However much energy was absorbed must be released again, but it can be released in smaller packets
A high energy photon might be absorbed, but two lower energy photons might be released as the electron falls in a “step-wise” manner.
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Photons must match energy changes
The energy of the photon must exactly match the energy change of the electron.
If the photon is not an exact match, the photon will pass through unabsorbed.
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Measuring light absorption
All colors of light go in
Sample of hydrogen
Not all colors come out
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The black bars are the colors that a hydrogen atom absorbs. The other colors pass through the atom un-absorbed.
Hydrogen Spectrum
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Absorption of Molecules
Because the structure of a molecule is much more complicated than a single atom, they absorb regions of light rather than single wavelengths.
Picture from http://www.lsbu.ac.uk/water/vibrat.html
Absorption spectrum of water
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Ways of producing light
Fluorescence: visible light is absorbed and visible light is emitted at the same time—the relaxation happens very quickly after excitation
Phosphorescence: Visible light is absorbed and then a while later is emitted—relaxation occurs after a period of time
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Ways of producing light
Incandescence: Energy is put in from heat and given off as visible light
Chemiluminescence: Energy released during a chemical reaction is absorbed to cause excitation. Relaxation produces visible light
Biolouminescence: Chemiluminescence that occurs in a biological organism.
Triboluminescence: Physical pressure or torque provides energy for excitation. Relaxation produces visible light.
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What did you learn about glowing things?
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Glow in the dark
Electron structure
Electron structure
Is based on
Atomic structure
Atomic structure
LightLight
Atomic theory
Atomic theory
PeriodicityPeriodicity
Is a part of
Gives off
Is based on
Periodic Table
Periodic Table
Arranged to show
Changes in produce
Which can be determined using