Kristin Chin, Shivam Patel
MP2 Project
Madigan – P7
Molecular Geometry and Lewis Structures
Molecular Geometry and Lewis Structures
Lewis Structure Key Terms:
Valence electrons: electrons on the outermost shell of an atom
- The Octet Rule: eight electrons in the valence shell (filling s and p orbitals) make an atom
stable.
Exceptions: Be - 2 bonds, B - 3 bonds, S - 6 bonds, P - 5 bonds, Xe – 6 bonds
- Bond Lengths: Triple Bond < Double Bond < Single Bond
- Bond Energy: Single Bond < Double Bond < Triple Bond
- Resonance Structures: one or two of more Lewis structures for a single molecule can be
drawn to represent a molecule.
- Formal Charge: the difference between the number of valence electrons. The sum of the
formal charges of the atoms in a molecule of ion must equal the charge on the molecule or ion.
Equation:
FC = total # of valence e- - total # of nonbonding e- - ½ (total # of bonding e-)
Steps for Drawing Lewis Dot Structures:
1. Draw skeletal structure of compound showing what atoms are bonded to each other. Put
least electronegative element in the center.
2. Count total number of valence electrons. Add 1 for each negative charge. Subtract 1 for
each positive charge.
3. Complete an octet for all atoms except hydrogen
4. If structure contains too many electrons, form double and triple bonds on central atom as
needed.
Draw the Lewis structures and using the table on the back, predict the molecular geometry and
label the bond angles for the following:
1. PO43-
2. CS2
2. SO42-
4. PH3
Kristin Chin, Shivam Patel
MP2 Project
Madigan – P7
Molecular Geometry and Lewis Structures
VSEPR Theory: Shows how molecules are actually arranged in a 3D setting
Predicting Molecular Geometry:
1. Draw Lewis structure for molecule PCl42. Count number of lone pairs on the central atom and number of atoms bonded to the
central atom
3. Use VSEPR to predict the geometry of the molecule
Number of Surrounding
Atoms
2
2
2
2
2
3
3
3
Number of Lone Pairs
Shape
Bond Angle
0
1
2
3
4
0
1
2
Linear
Bent
Bent
Linear
Linear
Trigonal Planar
Trigonal Pyramidal
T-Shaped
180
<120
104.5
180
180
120
107
90 and 180
3
3
T-Shaped
90 and 180
4
0
Tetrahedral
109.5
4
1
See-Saw
<90 and <120
4
2
Square Planar
90
5
0
Trigonal bipyramidal
120 and 90
5
1
Square Pyramidal
<90
6
0
Octahedral
90
Hybridization: mixing two or more atomic orbitals to form a new set of hybrid orbitals:
# of lone pair on central atom + # of atoms bonded to central atom
# of Bonded Atoms + # lone pairs
2
3
4
1. Determine the formal charge of :
a. ClF3
b. OH3+
2. Predict the hybridization of:
a. CO2
b. CF
Hybridization
sp
sp2
sp3
Examples
SiO2
BF3
CCl4
3. Draw the Lewis structures and any
resonance structures of:
a. NO2b. HNO3
4. Name to molecular geometry of:
a. XeOF4
b. SF5
Kristin Chin, Shivam Patel
MP2 Project
Madigan – P7
Molecular Geometry and Lewis Structures