1. Molecular Structure
Molecular Geometry

2. VSEPR theory
Valence-Shell Electron-Pair Repulsion Theory: Because electron pairs repel, molecules adjust their shapes so that valence electron pairs are as far apart as possible

3. Vsepr continued…
Types of electron pairs Bonding Pairs: Electrons that form bonds Lone (unshared) Pairs: Electrons that are nonbonding; no atom trying to bond. These are held closer to the atom they are associated with than bonding pairs. Lone Pairs Repel More Strongly Than Bonding Pairs!

4. Lone pair effects on bond angles
In methane there are no lone pair electrons so in the tetrahedral shape the bond angles are the expected In the ammonia molecule there is one lone pair. Since it has a stronger repulsion is closes the bond angle a little to 1070 In the water molecule there are 2 lone pairs each having greater repulsion causing the angle to close even more to angle.

5. Determining Molecular Shape
Draw the Lewis Diagram
Count up electron pairs on central atom.
double/triple bonds = ONE pair
Shape is determined by the # of bonding pairs and lone pairs.
Be Familiar With the Common Shapes & Their Bond Angles
See p.10 in CRM

6. Common shape-Linear
Beryllium Hydride 2 total electron pairs 2 bonding pairs 0 lone pairs Beryllium does not follow the octet rule. Beryllium is complete with 4 valence electrons Carbon dioxide Carbon does follow the octet rule fulfilling it through two double bonds in this case

7. Common shape-trigonal planar
Boron Hydride 3 total electron pairs 3 bonding pairs 0 lone pairs Boron is also an exception to the octet rule. Boron is complete with 6 valence electrons Formaldehyde 4 total electron pairs 4 bonding pairs Carbon does follow the octet rule, which is fulfilled by the double bond.

8. Common Shape - Bent
Ozone Generally O would have two bonding pairs which is seen by the upper O, the other two adjust so that all three can obey the octet rule Water 4 total pairs 2 bonding pairs 2 lone pair

9. Common shape-tetrahedral
Methane 4 total pairs 4 bonding pairs 0 lone pairs

10. Common shape-trigonal pyramidal
Ammonia 4 total pairs 3 bonding pairs 1 lone pair

11. Common shape- trigonal bipyramidal
Phosphorous pentachloride 5 total pairs 5 bonding pairs 0 lone pairs

12. Common shape - octahedral
Sulfur Hexafluoride 6 total pairs 6 bonding pairs 0 lone pairs

13. Molecular Structure
Molecular Polarity

14. Dipole Moment Direction of the polar bond in a molecule
Arrow points toward the more electronegative atom.

15. Determining Molecular polarity
Depends on - dipole moments - molecular shape

16. Polar & Nonpolar molecules
Nonpolar Molecules - dipole moments are symmetrical and cancel out Polar Molecules - dipole moments are asymmetrical and don’t cancel

17. Polar Molecules
Therefore, polar molecules have… - asymmetrical shape (lone pairs) or - asymmetrical atoms