IIIIII Molecular Geometry Molecular Structure. A. VSEPR Theory Valence Shell Electron Pair Repulsion Theory Electron pairs orient themselves so that.

I II III

Molecular Geometry

Molecular Structure

A. VSEPR Theory

Valence Shell Electron Pair Repulsion Theory

Electron pairs orient themselves so that valence electrons are as far apart as possible

A. VSEPR Theory

Types of e- Pairs Bonding pairs - form bonds Lone pairs - nonbonding e-

Lone pairs repel

more strongly than

bonding pairs!!!

A. VSEPR Theory Lone pairs reduce the bond angle

between atoms.

Bond Angle

Draw the Lewis Diagram. Count up e- pairs on central atom.

double/triple bonds = ONE pair (for shape purposes only!!)

Shape is determined by the # of bonding pairs and lone pairs.

Know the 8 common shapes & their bond angles!

B. Determining Molecular Shape

C. Common Molecular Shapes

2 total electron pairs

*2 bonding pairs

*0 lone pairs

LINEAR180°

BeH2

Note: Beryllium does not follow the octet rule. Beryllium is complete with 4 valence electrons

3 total electron pairs

*3 bonding pairs

*0 lone pairs

TRIGONAL PLANAR

120°

BF3

C. Common Molecular Shapes

Note: Boron is also an exception to the octet rule. Boron is complete with 6 valence electrons

C. Common Molecular Shapes

3 total pairs

*2 bonding pairs

*1 lone pair

BENT

<120°

SO2

4 total pairs

*4 bonding pairs

*0 lone pairs

TETRAHEDRAL

109.5°

CH4

C. Common Molecular Shapes

4 total pairs

*3 bonding pairs

*1 lone pair

TRIGONAL PYRAMIDAL

107°

NH3

C. Common Molecular Shapes

4 total pairs

*2 bonding pairs

*2 lone pairs

BENT

104.5°

H2O

C. Common Molecular Shapes

5 total pairs

*5 bonding pairs

*0 lone

TRIGONAL BIPYRAMIDAL

120°/90°

PCl5

C. Common Molecular Shapes

6 total pairs

*6 bonding pairs

*0 lone pairs

OCTAHEDRAL

90°

SF6

C. Common Molecular Shapes

PF3

4 total

3 bond

1 lone

TRIGONAL PYRAMIDAL

107°

F P FF

D. Examples

CO2

O C O2 total

2 bonding pairs

0 loneLINEAR

180°

D. Examples

I II III

Molecular Polarity

Molecular Structure

Molecular Polarity

• Polar Molecule: Molecule that has a partially positive end and a partially negative end. (It has electrical poles)

• There is an uneven distribution of electrons in the molecule

A. Dipole Moment

Direction of the polar bond in a molecule.

Arrow points toward the more electronegative atom.

H Cl+ -

B. Determining Molecular Polarity Depends on:

dipole moments molecular shape

B. Determining Molecular Polarity Nonpolar Molecules

Dipole moments are symmetrical and cancel out.

BF3

F

F F

B

B. Determining Molecular Polarity Polar Molecules

Dipole moments are asymmetrical and don’t cancel .

netdipolemoment

H2OH H

O

.. ..

B. Determining Molecular Polarity Polar molecules have...

asymmetrical shape (lone pairs) or

asymmetrical atoms (attached atoms are different)

B. Determining Molecular Polarity Nonpolar Molecules have…

No lone pairsAll attached atoms are the same