Transcript Chapter 12

Chapter 4
Spectroscopy
Kirchhoff’s First Law
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Hot, dense gases or solids produce a
continuous spectrum.
• Example: Light bulb filament
Continuous Spectrum
Kirchhoff’s Second Law
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Hot, rarefied gas produces an
emission line spectrum.
• Example: Neon sign
Emission Line Spectrum
Kirchhoff’s Third Law
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Cool gas in front of a continuous source of
light produces an absorption line spectrum.
• Example: The Sun
Absorption Spectrum
The Kirchhoff-Bunsen Experiment
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These two scientists found that burning
chemicals over an open flame resulted in a
spectrum with bright lines.
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They found that each chemical element
produced its own characteristic pattern of
bright spectral lines.
Structure of the Atom
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Proton
Neutron
Electron
Quantized Energy Levels
Excitation
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There are two ways to get electrons
excited.
– Add Heat to the Atoms
• This causes collisions.
– Shine Light on the Atoms
• Atoms can absorb light
De-excitation
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When an electron makes a transition to
a lower energy level a photon is
released.
Emission Spectra
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Spectral lines occur when an electron jumps from one
energy level to another.
Each chemical element produces its own unique pattern of
spectral lines.
Example Question
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What two things can you do to atoms to
cause electrons in the ground state to jump
to the first excited state?
– Add Heat
– Add Light
Matching Questions
Type of Spectrum
Appearance
1. Emission Spectra
a. All Colors
2. Continuous Spectra
b. Dark Lines
3. Absorption Spectra
c. Bright Lines
Matching Questions
1. Emission Spectra
a. Hot Solids
2. Continuous Spectra
b. Hot Stars
3. Absorption Spectra
c. Hot Thin
Gases
Spectra
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Absorption occurs when a photon causes
an electron to jump from a low energy
level to a high energy level.
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Emission occurs when a photon is emitted
after an electron jumps from a high energy
level to a low energy level.
Energy Carried by Light
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“High frequency radiation carries
proportionally more energy than low
frequency radiation”. - Page 92
E  hf
Compare these spectra.
Spectrum of Hydrogen in Lab
Spectrum a Star
What do these spectra tell us about the star?
Measuring a Star’s Composition
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Each atom absorbs a unique combination
of wavelengths of light.
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From this we can determine the
composition of a star.

Star’s are composed of mostly hydrogen.
Compare these spectra.
Spectrum of Hydrogen in Lab
Spectrum of a Star
What do these spectra tell us about the star?
Measuring a Star’s Motion
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The spectral lines of a star moving away
the Earth exhibit a redshift.
The spectral lines of a star moving toward
the Earth exhibit a blueshift.
These shifts are caused by the Doppler
effect.
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v

 c
Compare these spectra.
Spectrum of Hydrogen in Lab
Spectrum a Star…..Day 1
Spectrum a Star…..Day 2
Spectrum a Star…..Day 3
Spectrum a Star…..Day 4
What do these spectra tell us about the star?
Mystery Star Properties
1. The star appears as a point of light through a telescope.
2. The absorption lines appear split and move over a
4 day period.
3. The brightness of the star also varies over 4 days.
Question: Why do you think the brightness of the
star is varying?
Answer: This could be an eclipsing binary star
system that cannot be resolved by a
telescope!
Matching Questions
1. The temperature of a star can be determined from
its_____________.
2. The pattern of the absorption spectral lines for a star
contains information about a star’s________________.
3. The Doppler shift of a star's spectral lines tells us
something about the star’s_______________.
(a) composition
(b) motion
(c) color
End of Chapter 4