1. Bellwork Monday Draw the following Lewis dot structures. CCl4 NH4+
SO CN-
CO32-

2. Unit 11 Ch 7 & 8 Part 4
VSEPR
Covalent molecule shapes

3. VSEPR Valence Shell Electron Pair Repulsion theory
Valence electrons on the central atom repel each other.

4. VSEPR:
Regions of electron density (where pairs of electrons are found) can be used to determine the shape of the molecule.
CO2
Here there are two regions of electron density.
The regions want to be as far apart as possible, so it is linear. O C O

5. EXAMPLES: 1 4 2 3 H H C H H CH4 There are four electron pairs.
You would expect that the bond angles would be 90° but…
Because the molecule is three-dimensional, the angles are 109.5°.
The molecule is of tetrahedral arrangement. H C H 2 H 3

6. EXAMPLES: 1 4 2 3 Four regions of electron density
NH3
Four regions of electron density
But one of the electron pairs is a lone pair
The shape is called trigonal pyramidal H N H 2 H 3

7. EXAMPLES: 1 4 2 3 H2O Four regions of electron density
But two are lone pairs
This structure is referred to as bent H O H 2 3

8. [ ] EXAMPLES: 1 3 2 2- CO32- Three regions of electron density
[ ] 2-
CO32-
Three regions of electron density
This structure is referred to as trigonal planar O C O 2 O

9. Practice determining molecular shape:
H2S
4 regions of e- density
2 lone pairs
bent S H S H H H

10. Practice determining molecular shape:
SO2
3 areas of e- density
1 lone pair
bent O S S O O O

11. Practice determining molecular shape:
CCl4
4 areas of e- density
tetrahedral Cl 3d Cl C Cl Cl

12. Practice determining molecular shape:
BF3
3 areas of e- density
trigonal planar F F B F B F F F

13. Practice determining molecular shape:
NF3
4 areas of e- density
1 lone pair
pyramidal 3d F N F F