1. Molecular Geometry and VSEPR Theory

2. VSEPR Theory
To understand the shapes of molecules, we use a theory called the Valence Shell Electron Pair Repulsion Theory
This theory tells us how we can understand the geometry of a molecule by looking at the electron groups that surround it
Electron groups can be:
Single Bonds
Double Bonds (1 e- group)
Triple Bonds (1 e- group)
Lone Pairs (still 1 e- group)

3. VSEPR Theory
VSEPR Theory tells us that electron groups will repel each other
This is because of negative charges. A negative and a negative from the electrons will repel
The electron groups then move as far away from each other as possible
This will determine the shape of the molecules

4. Electron Group Geometries
Electron Group Geometries (EGG) are the shapes made when the electron groups repel
There are 5 basic electron group geometries
Linear (2 electron groups)
Trigonal Planar (3 electron groups)
Tetrahedral (4 electron groups)
Trigonal Bipyramidal (5 electron groups)
Octahedral (6 electron groups)

5. Linear Geometry
When 2 electron groups are around the central atom, the farthest away is 1800
This creates a linear shape
Example
Draw a molecule of CO2 and determine the EGG

6. Trigonal Planar
With 3 electron groups around the central atom, the farthest away for all electrons to be is 1200 in the same plane
Because they are in the same plane, the is called Trigonal Planar (3 in same plane)
Example
Draw a molecule of COCl2 and determine the EGG

7. Tetrahedral
With 4 Electron groups, the furthest point for electron groups is
This may seem weird since on paper is looks like 900 but remember, molecules are 3-dimensional and can make complex shapes
This shape forms a tetrahedron and is called Tetrahedral
Example
Draw a molecule of NH3 and determine the EGG

8. Trigonal Bipyramidal
5 electron groups around the central atom makes a Trigonal Bipyramidal structure
This is like 2 pyramids (bipyramidal) joined together
It also has 3 atoms atoms making a trigonal structure in it
These have 2 angles, 900 between the x-plane and the y-plane and 1200 in the x-plane
Example
Draw a molecule of PCl5 and determine the EGG

9. Octahedral With 6 electron groups an octahedral structure is formed
All angles are 900
Example
Draw a molecule of SF6 and determine the EGG

10. Molecular Geometry The EGG tells us the shape of ALL ELECTRON GROUPS
The molecular geometry is the geometry of the atoms
This is determined by the number of electron groups AND the number of bonds around a central atom

11. Molecular Geometries

12. Molecular Geometry Example
Draw a molecule of H2O
Determine the EGG
Use the chart provided to find the Molecular Geometry