1. Section 8.4 Molecular Shapes
Summarize the VSEPR bonding theory.
atomic orbital: the region around an atom’s nucleus that defines an electron’s probable location
Predict the shape of, and the bond angles in, a molecule.
Define hybridization.
VSEPR model
hybridization
The VSEPR model is used to determine molecular shape.

2. VSEPR Model
The shape of a molecule determines many of its physical and chemical properties.
Molecular geometry (shape) can be determined with the Valence Shell Electron Pair Repulsion model, or VSEPR model which minimizes the repulsion of shared and unshared electrons around the central atom.

3. VSEPR Model (cont.)
Electron pairs repel each other and cause molecules to be in fixed positions relative to each other.
Unshared electron pairs also determine the shape of a molecule.
Electron pairs are located in a molecule as far apart as they can be.

4. Lone pairs repel more strongly than bonding pairs!!!
VSEPR Theory
Types of e- Pairs (around central atom)
Bonding Areas - from bonds (single, double, triple) all count as one pair
Lone pairs - nonbonding e-
Lone pairs repel more strongly than bonding pairs!!!

5. Determining Molecular Shape
Draw the Lewis Diagram.
Tally up e- pairs on central atom.
Single/double/triple bonds = ONE pair (AREA)
Shape is determined by the # of bonding AREAS and LONE PAIRS.
Know the 8 common shapes
& their bond angles!

6. Common Molecular Shapes
e- Tally
2 total
2 bond areas
0 lone pairs
BeH2
LINEAR
180°

7. Common Molecular Shapes
e- Tally
3 total
3 bond areas
0 lone pairs
BF3
TRIGONAL PLANAR
120°

8. Common Molecular Shapes
e- Tally
4 total
4 bond areas
0 lone pairs
CH4
TETRAHEDRAL
109.5°

9. Common Molecular Shapes
e- Tally
4 total
3 bond areas
1 lone pair
NH3
TRIGONAL PYRAMIDAL
107°

10. Common Molecular Shapes
e- Tally
3 total
2 bond areas
1 lone pair
SO2
BENT
<120°

11. Common Molecular Shapes
e- Tally
4 total
2 bond areas
2 lone pairs
H2O
BENT
104.5°

12. Common Molecular Shapes
e- Tally
5 total
5 bond areas
0 lone pairs
PCl5
TRIGONAL BIPYRAMIDAL
120°/90°

13. Common Molecular Shapes
e- Tally
6 total
6 bond areas
0 lone pairs
SF6
OCTAHEDRAL
90°

14. F P F F 107° Examples TRIGONAL PYRAMIDAL 4 total 3 bond areas
1 lone pair
TRIGONAL PYRAMIDAL
107°

15. Examples
O C O
CO2
2 total
2 bond areas
0 lone pair
LINEAR
180°

16. Hybridization
Is the process by which s, p, and d orbitals combine to form new identical orbitals
The hybridization is equal to the total number of Bonding Areas and lone pairs around the central atom in the molecule.
For example: water has two bonding areas and two lone pairs of electrons, so we need 4 total hybrid orbitals = one s orbital and three p orbitals = sp3

17. Hybridization (cont.)
Single, double, and triple bonds occupy only one hybrid orbital (CO2 with two double bonds forms an sp hybrid orbital).

18. Hybridization (cont.)

19. Hybridization (cont.)

20. Hybridization (cont.)

21. A B C D Section 8.4 Assessment
The two lone pairs of electrons on a water molecule do what to the bond angle between the hydrogen atoms and the oxygen atom?
A. They attract the hydrogen atoms and increase the angle greater than 109.5°.
B. They occupy more space and squeeze the hydrogen atoms closer together.
C. They do no affect the bond angle.
D. They create resonance structures with more than one correct angle. A B C D

22. A B C D Section 8.4 Assessment
The sp3 hybrid orbital in CH4 has what shape?
A. linear
B. trigonal planar
C. tetrahedral
D. octahedral A B C D