1. Molecular Shapes: True shapes of molecules
Lewis Structure (2D)
Molecular Shape (3D) 2

2. Valence Shell Electron Pair Repulsion Theory
VSEPR Theory
Valence Shell Electron Pair Repulsion Theory
Main ideas – Electron pairs have repulsions of each other, but they have to be positioned as requested
Need to position these electron pairs as far as possible
As to minimize repulsions between electron pairs
Determines the shape of 3D molecule
1 Lone Pair = 2 Left Over e-
Look up:
1) Bonding vs Left over electron pairs on Different Atoms
2) Bonding vs Left over electron pairs on Central Atom
3) Left over electrons Pairs around Central Atom

3. Steps for Predicting Molecular Structures using VSEPR Model
Draw the Lewis Structure for the molecule.
Count the electron pairs and arrange them in the way that minimize repulsions (put the pairs as far apart as possible).
Determine the positions of the atoms from the way the electrons pairs are shared.
Determine the name of the molecular structure from the positions of the atoms.
Must Show 3-D shape by using and

4. Be Careful When Drawing Molecular Shapes
No Charge and No [ ] around the shape
Only Draw the Lone Central Atom
 Don’t draw the Left Over e- around other atoms
Bend when having Lone central atom
When Bending, Lone Pair stay on the top, Bonds stay on the bottom.
More Lone Central Atom  Bend More

5. Left Over e- (Lone Pair)
Lone Pair: Valence e- pair that is not involved in bonding Linear, Trigonal Planar, and Tetrahedral have NO lone pair around the central atoms

6. Left Over e- (Lone Pair) around Central Atoms
What about if there are lone pair around the central atom?
REMEMBER: Lone Pair (LP)
also take up space!!!
repel each other
repel bonded pairs
Use as lone central atom instead
of electron pairs.

7. 5 Molecular Shapes A) Linear (2 kinds) B) Trigonal Planar
C) Tetrahedral
D) Trigonal Pyramid
E) Bent (2 kinds)
Total Atoms = Central Atom + Bonded Atom ? Lone Pair
TA = CA + BA ? LP

8. A) Linear (2 kinds) Linear 2 Linear 1 2 TA = 0 CA + 2 BA, 0 LP
 angle = 180 degrees
 angle = 180 degrees
Linear 2
Linear 1

9. 4 TA = 1 CA + 3 BA, 0 LP  angle = 120 degrees
B) Trigonal Planar
4 TA = 1 CA + 3 BA, 0 LP  angle = 120 degrees

10. Need to draw and C) Tetrahedral 5 TA = 1 CA + 4 BA, 0 LP
Molecular Shapes
C) Tetrahedral
5 TA = 1 CA + 4 BA, 0 LP
angle = degrees
Need to draw and

11. Need to draw and D) Trigonal Pyramidal
4 TA = 1 CA + 3 BA, 1 LP  angle = degrees Remember, lone pairs take up space! (Use Oval)
107.2
Need to draw and

12. 3 TA = 1 CA + 2 BA, 1 LP  angle = 119.2 – 120 degrees
E) Bent (2 kinds)
3 TA = 1 CA + 2 BA, 1 LP  angle = – 120 degrees
3 TA = 1 CA + 2 BA, 2 LP  angle = 105 degrees
Bent 1
Bent 2
Need to draw
and