GEN CHEM 1 | VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) Theory

electrons surrounding atoms exert repulsive forces against each other, which means a molecule will take a shape where this will be minimized

Central Atom

Represented by A, it is where all the bonds are attached to.

Electron Groups

consists of bonding groups and lone pairs

Bonding Groups

Represented by X, these are the bonds formed between the central atom and the other atoms

Lone Pairs

Represented by E, these are pairs of electrons that did not form a bond

Linear Electron Geometry

2 electron groups; sp hybridization; 180º

Trigonal Planar Electron Geometry

3 electron groups; sp² hybridization; 120º

Tetrahedral Electron Geometry

4 electron groups; sp³ hybridization; 109.5º

Trigonal Bipyramidal Electron Geometry

5 electron groups; sp³d hybridization and 120º (in plane) and 90º (above and below plane) for all VSPER classes except linear which has 180º

Octahedral Electron Geometry

6 electron groups; sp³d² hybridization and 90º

Linear Molecular Geometry

• AX₂ (2 bonds, 0 lone pairs)

• AX₂E₃ (2 bonds, 3 lone pairs)

• AX₂E₄ (2 bonds, 4 lone pairs)

Trigonal Planar Molecular Geometry

AX₃ (3 bonds, 0 lone pairs)

Bent Molecular Geometry

• AX₂E (2 bonds, 1 lone pair)

• AX₂E₂ (2 bonds, 2 lone pairs)

Tetrahedral Molecular Geometry

AX₄ (4 bonds, 0 lone pairs)

Trigonal Pyramidal Molecular Geometry

AX₃E (3 bonds, 1 lone pair)

Trigonal Bipyramidal Molecular Geometry | Composition

AX₅ (5 bonds, 0 lone pair)

Seesaw Molecular Geometry | Composition

AX₄E (4 bonds, 1 lone pair)

T-Shaped Molecular Geometry | Composition

• AX₃E₂ (3 bonds, 2 lone pairs)

• AX₃E₃ (3 bonds, 3 lone pairs)

Octohedral Molecular Geometry | Composition

AX₆ (6 bonds, 0 lone pairs)

Square Pyramidal Molecular Geometry | Composition

AX₅E (5 bonds, 1 lone pair)

Square Planar Molecular Geometry | Composition

AX₄E₂ (4 bonds, 2 lone pairs)

Predicting Molecular Geometry

1. Draw the Lewis Structure of the molecule

2. Count the number of bonds and lone pairs based on the central atom. Write these as the AXE notation.

3. Determine the shape based on the given notation

4. Draw the molecule based on the shape.

What is the line if the bond is on the plane of the paper?

Straight line

What is the line if the bond is coming out of the page towards us?

Triangle

What is the line if the bond is going into the page away from us?

Broken line

What molecular geometry is shown here?

Linear

What molecular geometry is shown here?

Trigonal Planar

What molecular geometry is shown here?

Bent/Angular

What molecular geometry is shown here?

Tetrahedral

What molecular geometry is shown here?

Trigonal Pyramidal

What molecular geometry is shown here?

Trigonal Bipyramidal

What molecular geometry is shown here?

Seesaw

What molecular geometry is shown here?

T-Shape

What molecular geometry is shown here?

Octahedral

What molecular geometry is shown here?

Square Pyramidal

What molecular geometry is shown here?

Square Planar