1. Chapter 6 –The Shape of Molecules

2. Why Care About the Shape of Molecules
Shape determines molecular properties
Melting point
Boiling point
Chemical reactivity

3. All electrons are negatively charged. Like charges repel.
VSEPR Model
(Valence Shell Electron Pair Repulsion)
Theory that determines how molecules arrive at a three dimensional shape
Repulsion between the sets of valence-level electrons surrounding an atom causes these sets to be oriented as far apart as possible
All electrons are negatively charged.
Like charges repel.

4. Are These Bonds As Far Apart As Possible?
No Way! H H H C H H B H H

5. Predicting a VSEPR Structure
Draw Lewis structure.
Determine the number of electron groups around the central atom
1 electron group is equal to
Single, Double, Triple Bond or Lone Pair
Count up lone pairs on the central atom
Determine the shape of the molecule
Determine the bond angle

6. Base VSEPR Structure
2 Electron Groups
Linear
Bond angles of 180˚ X A

7. X A Base VSEPR Structure 3 Electron Groups Trigonal Planar
Bond angles of 120˚ X A

8. X A Base VSEPR Structure 4 Electron Groups Tetrahedral Geometry
Bond angles of 109.5˚

9. Determine shape and bond angles for
Your Turn
Determine shape and bond angles for
BI3
SiBr4
BeF2
Trigonal Planar, 120°
Tetrahedral, 109.5°
Linear, 180°

10. Lone Pairs of Electrons
Lone Pairs of Electrons make the bond angle a little bit smaller
More replusion

11. 1 Lone Pairs on Trigonal Planar
Bent – Bond Angles of < 120 A X X

12. 1 Lone Pair w/ Tetrahedral
Trigonal Pyramidal – Bond Angles 107 X A

13. 2 Lone Pairs w/ Tetrahedral
Bent – Bond Angles = 104.5 A X X

14. Determine shape and bond angles for
Your Turn
Determine shape and bond angles for
PBr3 O3
SeO2
Trigonal Pyrimidal, 107°
Bent, <120°
Bent, <120°

15. Intermolecular Forces
Forces of attraction between molecules
Intermolecular Forces are responsible for melting and boiling points
Strong IMF raise BP and MP
Three different types of IMF
London Forces, Dipole-Dipole, and Hydrogen Bonding

16. Permanent attraction between polar molecules
Dipole - Dipole
Permanent attraction between polar molecules

17. Extra Strong attraction b/t polar molecules where H is bonded to F,N,O
Hydrogen Bonding
Extra Strong attraction b/t polar molecules where H is bonded to F,N,O

19. Temporary Dipole caused by the collision of nonpolar molecules
London Forces
Temporary Dipole caused by the collision of nonpolar molecules