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Molecular Polarity Study Guide: Chapter 8 and 9 Exam Review

Prepare for your exam on Chapters 8 and 9 with this study guide. Learn about molecular polarity, valence bond theory, and hybrid orbitals. Video review and tips included.

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Molecular Polarity Study Guide: Chapter 8 and 9 Exam Review

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  1. December 2, 2009 EXAM #4 ON FRIDAY! CHAPTERS 8 AND 9 STUDY GUIDE AVAILABLE THIS AFTERNOON VIDEO REVIEW WILL BE POSTED TOMORROW TOPICS Molecular Polarity Review Valence Bond Theory (9.2)

  2. Is this molecule polar or nonpolar? • Polar • Nonpolar

  3. Is this molecule polar or nonpolar? • Polar • Nonpolar

  4. Is this molecule polar or nonpolar? • Polar • Nonpolar

  5. Is this molecule polar or nonpolar? • Polar • Nonpolar

  6. Molecular Polarity Tips Symmetrical molecules are nonpolar; asymmetry leads to polarity Hydrocarbons (CxHy) are nonpolar Molecules that have an –OH group are polar

  7. Chapter 9 Valence Bond Theory 2pz 2px 2py Video lecture review: Sigma bonds form when orbitals overlap In unbonded atoms, electrons are found in atomic orbitals (s, p, d, f, etc.) In bonded atoms, electrons are found in hybrid orbitals Hybrid geometries match VSEPR geometries Hybrid orbitals are “combinations” of atomic valence orbitals 2s Orbitals in CH4 Orbitals on C

  8. Types of Hybrid Orbitals

  9. Types of Hybrid Orbitals: 2 Pairs You get this: Starting with this: Two atomic orbitals make two hybrid orbitals

  10. Types of Hybrid Orbitals: 3 Pairs You get this: Starting with this: Three atomic orbitals make three hybrid orbitals

  11. Types of Hybrid Orbitals: 4 Pairs

  12. Say you have a molecular formula…what do you do next? • Draw the Lewis structure! • Count the structural electron pairs (sep) • Use the # of sep’s to determine hybrid orbital type • Remember that the # of hybrid orbitals = # sep’s • For example: Ethylene, C2H4 Each carbon has 3 sep’s sp2 hybrid orbitals (3 of them)

  13. Hybrid orbitals are used for sigma bonds and lone pairs • Unhybridized orbitals are used for the other type of bond- the pi bond- or they stay empty. • Examples: • NH3 • CH2O (note: terminal atoms don’t hybridize, just central atom)

  14. Pi Bonding • Uses unhybridized p orbitals • Ethene:

  15. Pi Bond Formation Two areas of overlap = 1 pi bond

  16. Bonding in Acetylene 2 sep’s => yields 2 sp hybrid orbitals, 2 unhybridized p orbitals left over

  17. Bonding in Formaldehyde

  18. Acetonitrile • What is the hybridization of C1? • sp3 • What is the hybridization of C2? • sp • How many sigma () and how many pi () bonds? • 5  bonds, 2  bonds • Multiple bonds  First bond is sigma, the rest are pi 2 1

  19. Bonding in Benzene

  20. Advanced: Allene Each end carbon is a flat trigonal. Are they co-planar or perpendicular?

  21. Bonding in Allene

  22. Conformations vs. Isomers • Isomers: Molecules with same formula but different structure • Conformers: Different temporary shapes of the same molecule

  23. Bond Rotations • CAN happen around single bonds • Cannot happen around double bonds

  24. Cis-Trans Isomerization When two groups are on a “side” of a molecule. cis trans

  25. Can these molecules have cis-trans isomers?

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