Chapter 3 part 2a - Review So Far The shape of a molecule...

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1 Chemistry in Context Chapter 3 Part 2 The Chemistry of Global Warming Review So Far • The shape of a molecule is determined from Lewis diagrams and RHED. • Whether a molecule is IR active depends, in part, on its shape. • IR active molecules absorb IR waves of a higher energy then re-emit waves of a lower energy. Review So Far • Chemistry Topics: – Lewis dot diagrams and Lewis line diagrams – Octet rule and exceptions to the octet • Less than octet • Expanded octet • Ions – Calculations involving E, v, λ , c, h. Note • Electronegativity and polarity will be covered on a later date.
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2 Today’s Focus Areas • Infrared radiation, IR spectra, IR active • Average molecular mass • Moles Recall • In order for a vibrational mode to be infrared active, it must change the molecule’s dipole moment. Question Which of the following diatomic molecules will be infrared active? 1) O 2 2) N 2 3) Cl 2 4) H 2 5) All of them 6) None of the other answers are correct Question • You know these are IR active: –H 2 O –CO 2 • Which of the following molecules would you expect to have at least one infrared active vibrational mode? –N 2 –A r –SO 2 –O
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3 Common Infrared Stretching and Bending Infrared Spectrum • How an IR works: – Radiation source – Beam passes through sample – Sample absorbs a portion of the beam, depending on the sample’s molecules and vibrational modes – Leftover beam goes to detector – Graph is plotted (insert IR spectrum) • From textbook Question • Why would scientists choose to use inverse wavelength as the X-axis, instead of wavelength?
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This note was uploaded on 05/10/2008 for the course CH 304k taught by Professor Walker during the Spring '08 term at University of Texas at Austin.

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Chapter 3 part 2a - Review So Far The shape of a molecule...

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