Wize High School Grade 11 Chemistry Textbook > Chemical Bonding
Valence Shell Electron Pair Repulsion Theory (VSEPR)
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Valence Shell Electron Pair Repulsion Theory (VSEPR)
- The VSEPR theory states that repulsion of electron groups (lone pairs and bonds) in the valence shell will determine the 3D geometry of a molecule.
- In VSEPR theory, we focus on the number of electron groups around a central atom.
- Bonding groups
- Non-bonding groups
- To draw a VSEPR structure, you need the Lewis structure and the number of electron groups.
- Wedges mean the bond is coming out of the page
- Dashes mean the bond is going into the page
- We use all the electron groups to get the electron-pair geometry.
- To get the molecular geometry, we look at the atoms present
Wize Concept
- Draw Lewis structure
- Determine the electron-group geometry based on the total electron groups
- Two electron groups: linear
- Three electron groups: trigonal planar
- Four electron groups: tetrahedral
- Determine the molecular geometry that minimizes repulsions
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Example: VSEPR Shapes
Determine the electron pair arrangement and molecular geometry for NH3
Electron geometry: tetrahedral
Molecular shape: trigonal pyramidal
Practice: VSEPR Terms and Definitions
The VSEPR model includes several concepts related to atomic theory. Match the following terms and definitions.
A.
a pair of electrons that is not involved in bonding
B.
a shared pair of electrons
C.
the outermost energy level or orbit of an atom or ion
D.
all pairs of valence electrons repel each other
valence shell
bonding pair
lone pair
electron pair repulsion
Practice VSEPR Shapes
For the following molecular geometries, fill in the table below with:
- the total number of electron groups
- the number of lone pairs on the central atom
- the number of bonding groups
| Molecular Geometry | Total number of electron groups | Number of lone pairs around the central atom | Number of bonding groups |
| Linear | |||
| Trigonal Planar | |||
| Bent | |||
| Trigonal Pyramidal | |||
| Tetrahedral |
Practice: Determining Electron Pair Arrangement and Molecular Geometries
Use the VSEPR theory with the following molecules to answer the following questions.
- PF3
- NH4+
- H2S
Which molecule has a tetrahedral electron pair arrangement?