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REVCHM11509 - CHM 115 Review From Spectroscopy to Polymers...

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1 CHM 115 Review From Spectroscopy to Polymers
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Energy (“light”) + Matter (molecules) region of spectrum wavelength range molecular effects …and this means… gamma pm – nm ionizing damage DNA UV-C 200-280 nm break bonds Highly damaging; totally absorbed by O 2 and O 3 in upper atmosphere UV-B 280-320 nm break bonds Sunburn and skin cancer. Absorbed by O 3 in stratosphere. UV-A 320-400 break bonds/ electron transitions A lot reaches surface of earth through atmosphere; can result in eye damage; tanning Visible 400-700 nm electron transitions Results in color IR (near) 700-5000 nm bond vibrations spectroscopy to look at structures of molecules Microwave 1 mm – 1 m bond rotations Microwave ovens
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3 How do we see stuff that is colored? White Light Wavelengths  we don’t see  because they  are absorbed We see the wavelengths that  get reflected (or transmitted) demo
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4 Spectroscopy Different molecules can absorb light of different colors (energies).
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5 Absorption depends on concentration
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6 Absorption depends on concentration Absorbance = ε × l × C   ε = molar absorptivity l = path length C = concentation The next two laboratory experiments deal with absorption of visible light and determination of concentration.
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7 Atoms bonded together are not stationary, they vibrate. Bonds stretch and angles bend. Simple model: two atoms connected by a spring Adding energy (via IR absorption) makes the atoms vibrate with more energy; the vibrational energies are quantized (just like n levels in atoms) Molecular Vibrations: IR Absorption http:// icn2.umeche.maine.edu/genchemlabs /IR/
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8 Interpreting IR stretching frequencies For the same elements, larger mass atoms will vibrate at a lower frequency (more slowly) (spring demo) The C-D stretching frequency is lower than the C- H stretching frequency. So, what would that indicate about the relative wavelengths?
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