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Understanding Molecular Structure and Polarity

Learn about molecular structure, molecular geometry, and VSEPR theory. Discover the different shapes of molecules and how to determine their polarity.

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Understanding Molecular Structure and Polarity

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  1. Molecular Structure Molecular Geometry

  2. A. VSEPR Theory • Valence Shell Electron Pair Repulsion Theory • Electron pairs orient themselves so that valence electrons are as far apart as possible

  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 8 common shapes & their bond angles! B. Determining Molecular Shape • Draw the Lewis Diagram. • Count 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 electron pairs *2 bonding pairs *0 lone pairs Note: Beryllium does not follow the octet rule. Beryllium is complete with 4 valence electrons LINEAR 180°

  7. BF3 C. Common Molecular Shapes 3 total electron pairs *3 bonding pairs *0 lone pairs TRIGONAL PLANAR 120° Note: Boron is also an exception to the octet rule. Boron is complete with 6 valence electrons

  8. SO2 C. Common Molecular Shapes 3 total pairs *2 bonding pairs *1 lone pair BENT <120°

  9. CH4 C. Common Molecular Shapes 4 total pairs *4 bonding pairs *0 lone pairs TETRAHEDRAL 109.5°

  10. NH3 C. Common Molecular Shapes 4 total pairs *3 bonding pairs *1 lone pair TRIGONAL PYRAMIDAL 107°

  11. H2O C. Common Molecular Shapes 4 total pairs *2 bonding pairs *2 lone pairs BENT 104.5°

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

  13. SF6 C. Common Molecular Shapes 6 total pairs *6 bonding pairs *0 lone pairs 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 bonding pairs 0 lone LINEAR 180°

  16. Molecular Structure Molecular Polarity

  17. Molecular Polarity • Polar Molecule: Molecule that has a partially positive end and a partially negative end. (It has electrical poles) • There is an uneven distribution of electrons in the molecule

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

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

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

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

  22. B. Determining Molecular Polarity • Polar molecules have... • asymmetrical shape (lone pairs) or • asymmetrical atoms (attached atoms are different)

  23. B. Determining Molecular Polarity • Nonpolar Molecules have… • No lone pairs • All attached atoms are the same

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