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II. Molecular Geometry

Ch. 9 – Molecular Structure. II. Molecular Geometry. A. VSEPR Theory. V alence Shell Electron Pair Repulsion Theory Electron pairs orient themselves in order to minimize repulsive forces. Lone pairs repel more strongly than bonding pairs!!!. A. VSEPR Theory. Types of e - Pairs

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II. Molecular Geometry

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  1. Ch. 9 – Molecular Structure II. Molecular Geometry

  2. A. VSEPR Theory • Valence Shell Electron Pair Repulsion Theory • Electron pairs orient themselves in order to minimize repulsive forces.

  3. Lone pairs repel more strongly than bonding pairs!!! A. VSEPR Theory • Types of e- Pairs • Bonding pairs - form bonds • Lone pairs - nonbonding e-

  4. Bond Angle A. VSEPR Theory • Lone pairs reduce the bond angle between atoms.

  5. Know the common shapes & their bond angles! B. Determining Molecular Shape • Draw the Lewis Diagram. • Tally up e- pairs on central atom. • double/triple bonds = ONE pair • Shape is determined by the # of bonding pairs and lone pairs.

  6. BeH2 C. Common Molecular Shapes 2 total 2 bond 0 lone LINEAR 180°

  7. BF3 C. Common Molecular Shapes 3 total 3 bond 0 lone TRIGONAL PLANAR 120°

  8. SO2 C. Common Molecular Shapes 3 total 2 bond 1 lone BENT 104.5°

  9. CH4 C. Common Molecular Shapes 4 total 4 bond 0 lone TETRAHEDRAL 109.5°

  10. NH3 C. Common Molecular Shapes 4 total 3 bond 1 lone TRIGONAL PYRAMIDAL 107°

  11. H2O C. Common Molecular Shapes 4 total 2 bond 2 lone BENT 104.5°

  12. PCl5 C. Common Molecular Shapes 5 total 5 bond 0 lone TRIGONAL BIPYRAMIDAL 120°/90°

  13. SF6 C. Common Molecular Shapes 6 total 6 bond 0 lone OCTAHEDRAL 90°

  14. F P F F D. Examples • PF3 4 total 3 bond 1 lone TRIGONAL PYRAMIDAL 107°

  15. OCO D. Examples • CO2 2 total 2 bond 0 lone LINEAR 180°

  16. C. Bond Polarity • Electronegativity Trend • Increases up and to the right.

  17. + - H Cl A. Dipole Moment • Direction of the polar bond in a molecule. • Arrow points toward the more e-neg atom.

  18. B. Determining Molecular Polarity • Depends on: • dipole moments • molecular shape

  19. F BF3 B F F B. Determining Molecular Polarity • Nonpolar Molecules • Dipole moments are symmetrical and cancel out.

  20. O net dipole moment H2O H H B. Determining Molecular Polarity • Polar Molecules • Dipole moments are asymmetrical and don’t cancel .

  21. H net dipole moment CHCl3 Cl Cl Cl B. Determining Molecular Polarity • Therefore, polar molecules have... • asymmetrical shape (lone pairs) or • asymmetrical atoms

  22. C. Bond Polarity • Most bonds are a blend of ionic and covalent characteristics. • Difference in electronegativity determines bond type.

  23. EN Difference • 0.0 - 0.4 Nonpolar • 0.4 - 1.0 Moderately Polar Covalent • 1.0 - 2.0 Very Polar Covalent • > 2.0 Ionic

  24. C. Bond Polarity Examples: • Cl2 • HCl • NaCl 3.0-3.0=0.0 Nonpolar 3.0-2.1=0.9 Moderately Polar Covalent 3.0-0.9=2.1 Ionic

  25. C. Bond Polarity • Electronegativity • Attraction an atom has for a shared pair of electrons. • higher e-neg atom  - • lower e-neg atom + ____

  26. C. Bond Polarity • Nonpolar Covalent Bond • e- are shared equally • symmetrical e- density • usually identical atoms

  27. - + C. Bond Polarity • Polar Covalent Bond • e- are shared unequally • asymmetrical e- density • results in partial charges (dipole)

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