1. Molecular Geometry
Chapter 6.5

2. VSEPR THEORY Lewis Structures are 2D but we live in a 3D world.
molecular geometry: the three-dimensional arrangement of a molecule’s atoms
What do those 3D structure/shapes look like??
Follow the Valance Shell Electron Pair Repulsion Theory or VSEPR
Following VSEPR allows us to predict bond polarity:
uneven distribution of electrons

3. Atoms bonded to central atom Number of Lone Pairs (on central)
AB2 – Linear
Central atom
Atoms/group of atoms attached to central atom
Atoms bonded to central atom
Number of Lone Pairs (on central)
Bond Angle 2
180˚ Cl Be

4. Other Linear Geometries
The shape of two atoms bonded together is not given in the chart.
Ex: F2
What is the only possible shape a binary compound can have?
LINEAR!

5. Atoms bonded to central atom
AB2E1 – Bent
Lone pairs of electrons on central atom (only)
Atoms bonded to central atom
Number of Lone Pairs
Bond Angle 2 1
<120˚
What happens to the bond angle between atoms as you increase the number of “lone pair electrons” on the central atom?
Bond angles decrease!

6. Atoms bonded to central atom
AB2E2 – Bent
Atoms bonded to central atom
Number of Lone Pairs
Bond Angle 2
104.5˚

7. Atoms bonded to central atom
AB3 – Trigonal Planar
Atoms bonded to central atom
Number of Lone Pairs
Bond Angle 3
120˚

8. AB3E1 – Trigonal Pyramidal
Atoms bonded to central atom
Number of Lone Pairs
Bond Angle 3 1
107˚

9. Atoms bonded to central atom
AB4 – Tetrahedral
Atoms bonded to central atom
Number of Lone Pairs
Bond Angle 4
109.5˚

10. Why use VSEPR Theory?
Key Point: VSERP Theory is used to predict the shape of molecules based on the fact that electron pairs strongly repel each other.

11. Predicting Molecular Geometry
Draw Lewis structure for molecule.
Count number of lone pairs on the central atom and number of atoms bonded to the central atom.
Use VSEPR to predict the geometry of the molecule.
What are the molecular geometries of SO2 and SF4? S F S O
AB4E
AB2E
tetrahedral
bent