1. Warm up
Draw lewis structures for the compounds below:
CF4
BF3
CO2

2. The 3D Shapes of Molecules
VSEPR Theory
The 3D Shapes of Molecules

3. VSEPR Theory Valence Shell Electron Pair Repulsion
Predicts the 3D geometry of molecules
The structure of covalent bonds around an atom is determined by minimizing electron-pair repulsions
Get electrons as far apart as possible!
Base structure depends on how many electron domains there are in the molecule
Molecule geometry depends on how many bonding pairs there are

4. Bond Lengths Bond length increases as atomic radius increases
Bond length decreases with multiple bonds:
Single > Double > Triple
Remember: Bond strength increases as bond length decreases

5. Turn to back of your notes
We will finish the front in a little bit!

6. 4 Electron Domains CF4 NCl3 H2Se Tetrahedral: CF4
Trigonal Pyramidal: NCl3
Bent: H2Se
H2Se

7. 3 Electron Domains
BF3
Trigonal Planar: BF3
Bent: NOH
NOH

8. 2 Electron Domains All diatomic compounds are linear
C2H2
Linear: C2H2
All diatomic compounds are linear
Most compounds with double or triple bonds are linear

9. Bond Angles Shape Angle of Bond Tetrahedral (4 e- regions) 109.5° CF4
Trigonal Pyramidal (4 e- regions)
<109.5° NCl3
Bent (4 e- regions)
<109.5° H2Se
Trigonal Planar(3 e- regions)
120° BF3
Linear (2 e- regions)
180° NOH

10. Bond Polarity Some molecules that have polar bonds are nonpolar!
If the dipole arrows cancel each other out, then the molecule does not have an overall dipole and will be nonpolar.
Examples: CO2, BF3, CF4
Example: CO2, BF3, CF4

12. Warm-Up
Draw the Lewis dot structures (see your notes) WITH dipole arrows for the following 3 molecules.
Carbon Dioxide
Boron Trifluoride
Carbon Tetrafluoride