1. VSEPR Theory
Atoms in a molecule try to spread out from one another as much as possible

2. methane, CH4
You might think this is the farthest that the hydrogens can get away from each other
109.5°
90°
In 3 dimensions, this shape actually causes less repulsion between the bonding pairs of electrons

3. Here are the STEPS for determining molecular geometry:
1. Draw a Lewis structure
2. Count the # of bonds and # of lone pairs around the central atom (these are called “domains”)
Single, Double and Triple bonds count as ONE domain (bonding domains)
Each lone pair counts as ONE domain (non-bonding domains)
3. Determine shape
Name of molecule shape is based on position of atoms (not domains)

5. How many “domains” around each central atom?

6. VSEPR Example

7. VSEPR Example

8. VSEPR Example

9. NOTE:
Lone pairs also want to be next to each other if they can be.

10. Now, Let’s Combine VSEPR with Polarity…..

11. If two atoms share electrons, but don’t share them equally, we call it a polar bond or “dipole moment”
Electrons are pulled closer to the more electronegative atom
One end of the molecule develops a partial negative charge because it has a higher electron density

12. Dipole Moments
ALL molecules with a lone pair on the central atom are polar.
Double bonds, even resonance, will lead to polarity

13. Water is Polar It has polar H-O bonds Its geometry is “bent”
So the molecule is polar
It has a dipole

14. BF3 is Non-polar It has polar B-F bonds
Its geometry is “trigonal planar”
So the molecule is non-polar
It does NOT have a dipole
All the fluorines “cancel”