Atomic Spectra

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Atomic Spectra

• Lab 1

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Light
If we pass light through a prism or diffraction
grating, we can see the intensity as a function
of wavelength.
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Type of Spectrum
Solids, liquids, and dense gases emit light of
all wavelengths, without any gaps or a
continuous spectrum
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• Thin gases emit light of only a few wavelengths -
  an emission or bright line spectrum.

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• If there is a source of light behind it, a thin
  gas will absorb light of the same wavelengths it
  emits
• this is called an absorption or dark line
  spectrum.

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Different Emission Line Spectra
H
He
C
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Balmer lines

• each element generates its own unique set of
  wavelengths of emission or absorption
• Balmer studied the optical spectrum of hydrogen
  and found a pattern in the wavelengths of its
  emission lines

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Periodic Table of Elements
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Balmer series set of visible lines in H spectrum

• For H, the wavelengths are - 374.9 377.0
  379.7 383.4 388.8 396.9 410.1 433.9
  486.0 656.1
• a simple formula reproduces these wavelengths
• ? (n) (364.5 nm ( n2 /n2 4))
• where n 3, 4, 5, ..

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other scientists found similar patterns in other
portions of the electromagnetic spectrum
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Paschen series

• Paschen, in the infrared, measured lines with
  wavelengths
• 866.2 874.8 886.0 901.2 922.6 954.3
  1004.6 1093.5 1281.4 1874.5 which matched the
  series
• ? (n) (820.5 nm ( n2 /n2 9))
• where n 4, 5, 6, ..

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Lyman series

• Lyman, in the ultraviolet, a series of lines with
  wavelengths
• 91.9 92.1 92.3 92.6 93.0 93.7
  94.9 97.2 102.5 121.5 corresponding to
  the series
• ? (n) (91.1 nm ( n2 /n2 1))
• where n 2, 3, 4, ..

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• In fact, scientists soon realized that hydrogen's
  spectrum could be broken down into a large number
  of series, each of which had wavelengths obeying
  a formula like
• ? (n,k) (limit) ( n2 /n2 k2)) where nkI,
  k2,.
• The Lyman series corresponds to k1 with a limit
  of 91.1 nm, the Balmer series to k2 with a limit
  of 364.5 nm, and so forth