© 2010 pearson education, inc. range of visible light our eyes can see from 400 (blue/purple) to...
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© 2010 Pearson Education, Inc.
Range of Visible Light
• Our eyes can see from 400 (blue/purple) to 700 (red) nm.
• Nm = nanometers = 10-9 meters
• Our eyes are most sensitive to yellow/green since that is the color of our sun
© 2010 Pearson Education, Inc.
© 2010 Pearson Education, Inc.
Continuous Spectrum
• The spectrum of a common (incandescent) light bulb spans all visible wavelengths, without interruption.
© 2010 Pearson Education, Inc.
Emission Line Spectrum
• A gas cloud emits light only at specific wavelengths that depend on its composition and temperature, producing a spectrum with bright emission lines.
© 2010 Pearson Education, Inc.
Absorption Line Spectrum
• A cloud of gas between us and a light bulb can absorb light of specific wavelengths, leaving dark absorption lines in the spectrum.
© 2010 Pearson Education, Inc.
How does light tell us what things are made of?
© 2010 Pearson Education, Inc.
Chemical Fingerprints
• Each type of atom has a unique set of energy levels.
• Each transition corresponds to a unique photon energy, frequency, and wavelength.
Energy levels of hydrogen
© 2010 Pearson Education, Inc.
© 2010 Pearson Education, Inc.
• Downward transitions produce a unique pattern of emission lines.
Chemical Fingerprints
© 2010 Pearson Education, Inc.
• Because those atoms can absorb photons with those same energies, upward transitions produce a pattern of absorption lines at the same wavelengths, producing an absorption spectrum.
Chemical Fingerprints
© 2010 Pearson Education, Inc.
Chemical Fingerprints
• Various emission spectra.
© 2010 Pearson Education, Inc.
Clicker Question
Which letter labels the peak (greatest intensity) of infrared light?
© 2010 Pearson Education, Inc.
Clicker Question
Which letter labels the peak (greatest intensity) of infrared light?
© 2010 Pearson Education, Inc.
Clicker Question
Which letter labels emission lines?
© 2010 Pearson Education, Inc.
Clicker Question
Which letter labels emission lines?
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