Chemical Bonding andMolecular Geometry

Valence-Shell Electron-Pair Repulsion (VSEPR) Theory

- Electron pairs repel each other, both bond pairs and unshared (lone pairs)

- Electron pairs assume orientations that minimize repulsions.

Applying VSEPR Theory1.Draw a Lewis structure 2.Determine the number of electron groups around the central atom and identify them as being either bond pairs or lone pairs.3.Establish the electron group geometry around the central atom-linear,trigonal-planar,tetrahedral4.Determine the molecular geometry from the positions around the central atom occupied by the other atomic nuclei.

Valence shell electron pair repulsion (VSEPR) model:

Predict the geometry of the molecule from the repulsions between the electron (bonding and nonbonding) pairs.

2 0

# of atomsbonded to

central atom

# lonepairs on

central atomArrangement of electron pairs

MolecularGeometry

10.1

linear linear

B B

Cl ClBe

2 atoms bonded to central atom0 lone pairs on central atom

10.1

2 0 linear linear

# of atomsbonded to

central atom

# lonepairs on

central atomArrangement of electron pairs

MolecularGeometry

VSEPR

3 0trigonal planar

trigonal planar

10.1

10.1

# of atomsbonded to

central atom

# lonepairs on

central atomArrangement of electron pairs

MolecularGeometry

VSEPR

3 0trigonal planar

trigonal planar

2 1trigonal planar

bent

10.1

2 0 linear linear

# of atomsbonded to

central atom

# lonepairs on

central atomArrangement of electron pairs

MolecularGeometry

VSEPR

3 0trigonal planar

trigonal planar

10.1

4 0 tetrahedral tetrahedral

10.1

# of atomsbonded to

central atom

# lonepairs on

central atomArrangement of electron pairs

MolecularGeometry

VSEPR

3 1

4 0 tetrahedral tetrahedral

tetrahedraltrigonal

pyramidal

10.1

10.1

GenericFormula

     

Number of Places

Where Electrons

 are Found

     Molecular  Shape

    Hybridiz

ation

MX 1 linear ---

MX2 2 linear sp

MX3 3trigonal planar

sp2

MX2E 3bent (angular, v-shaped)

sp2

MX4 4 tetrahedral sp3

MX3E 4trigonal pyramidal

sp3

MX2E2 4bent (angular, v-shaped)

sp3

MX5 5trigonal bipyramidal

sp3d

MX4E 5

seesaw (distorted tetrahedral)

sp3d

MX3E2 5 T-shaped sp3d

MX2E3 5 linear sp3d

MX6 6 octahedral sp3d2

MX5E 6square pyramidal

sp3d2

MX4E 6square planar

sp3d2

Hybrid Atomic Orbitals (1931 - Linus Pauling) •Proposed that the outermost (valence) orbitals of an atom could be combined to form hybrid atomic orbitals.

Sigma bond (

The end-to-end overlapping of an s orbital with a p orbital to form a sp hybrid orbital. Pi bond (

) - The side-to-side overlapping of two p orbitals. •Single bonds are made up of one sigma bond. •Double bonds are made up of one sigma bond and one pi bond. •Triple bonds are made up of one sigma bond and two pi bonds. Hybridization - A mixture of two or more atomic orbitals.