Valence Shell Electron Pair Repulsion Model
Tags
Chem/Molecule
Cegep/2
Word count
262 words
Reading time
2 minutes
Molecular geometry modelAbbr.
VSEPR model
Rules:
- Can be applied to any resonance model
- Only consider the central atom
= central atom = bonding electron pairs = lone electron pairs
- Electron pairs:
- Determine shape of molecule
- Double and triple bonds considered as single bonds
- Repel each other to be as far apart as possible
- Lone pairs repel more strongly than bonding pairs
Steps:
- Draw Lewis structure
- Recognize the VSEPR model
Class of molecule | # electron pairs | # bonding pairs | # lone pairs | Arrangement | Molecular geometry |
---|---|---|---|---|---|
2 | 2 | 0 | Linear | Linear | |
3 | 3 | 0 | Trigonal planar | Trigonal planar | |
3 | 2 | 1 | Trigonal planar | Bent | |
4 | 4 | 0 | Tetrahedral | Tetrahedral | |
4 | 3 | 1 | Tetrahedral | Trigonal pyramidal | |
4 | 2 | 2 | Tetrahedral | Bent | |
5 | 5 | 0 | Trigonal bipyramidal | Trigonal bipyramidal | |
5 | 4 | 1 | Trigonal bipyramidal | Distorted tetrahedron | |
5 | 3 | 2 | Trigonal bipyramidal | T-shaped | |
5 | 2 | 3 | Trigonal bipyramidal | Linear | |
6 | 6 | 0 | Octahedral | Octahedral | |
6 | 5 | 1 | Octahedral | Square pyramidal | |
6 | 4 | 2 | Octahedral | Square planar |
Examples
Predict the arrangement of electron pairs, the geometry and polarity of:
- Arrangement: trigonal bipyramidal
- Molecular geometry: linear
- Non-polar because it has rotational symmetry
- Arrangement: trigonal planar
- Molecular geometry: trigonal planar
- Polar because hydrogen breaks rotational symmetry