Lewis Structures and Molecular Geometry
Lab Activity
Procedure:
Part A:
1. Write the formula for each molecule or polyatomic ion listed in Data Table A. Some of the formulas
have been filled in for you.
2. Count the number of valence electrons supplied by each atom in the formula. Determine the total
number of valence electrons and record this number in Data Table A. In the case of polyatomic ions, add
on electron for each negative charge or subtract on electron for each positive charge.
3. Draw Lewis structures for each molecule in part A
Part B:
4. Examine the molecular models A – K. For each model, identify the number of bonding pairs, the number
of unshared pairs and the total number of electron pairs around the central atom. Record this information
in Data Table B
a. NOTE: In the case of double or triple bonds, count all of the electrons involved in the bond as
ONE PAIR
5. Sketch the three-dimensional arrangement of valence electron pairs around the central atom in Data table
B
6. Use the following terms to describe the molecular geometry for each model:
a. Linear, Bent, Trigonal pyramidal, tetrahedral, trigonal bipyramidal, octahedral
b. Record the molecular geometries for each molecule in the data table
Part C:
7. Compare the lewis structures in Data Table A to the molecular Geometry sketches in Data Table B.
Count the number of valence electron pairs (see step 4) around the central atom and predict the
molecular geometry for each molecule or ion in Data Table A.
8. In Data Table A, Draw a 3-D sketch of the molecule or ion in the space below its name and identify its
molecular geometry.
Sample 3-D drawings
H2O could be shown as this
while H3O+ could be shown as this
Lewis Structures and Molecular Geometry
Data Table A
Name
Molecular
Formula
Methane
CH4
Chlorine (diatomic!)
Sulfur Hexafluoride
Ammonia
Ammonium ION
Hydrogen Sulfide
H2S
Valence Electrons
Lewis structure
Lewis Structures and Molecular Geometry
Data Table A (con’t)
Name
Molecular
Formula
Sulfite ION
Arsenic Pentafluoride
Phosphorus Trichloride
Carbon Tetrachloride
Thiocyanate ION
SCN-1
Sulfate ION
Valence Electrons
Lewis structure
Lewis Structures and Molecular Geometry
Data Table B:
Model
Bonding
Pairs* #
Unshared
Pairs*
Total Pairs
Sketch and Molecular Geometry
A
B
C
D
E
F
G
*Count the bonding and nonbonding PAIRS of electrons around the central atom ONLY
# In the case of double or triple bonds, count them as ONE PAIR
Lewis Structures and Molecular Geometry
TEACHERS NOTES – Model Kits
Model
Bonding
Pairs* #
Unshared
Pairs*
Total Pairs
Sketch and Molecular Geometry
A
2
0
2
CO2 (double bonds)
Linear
B
4
0
4
Tetrahedral
C
3
1
4
Trigonal pyramidal
D
2
2
4
Bent
E
1
3
4
Linear (terminal)
F
5
0
5
Trigonal Bipyramidal
G
6
0
6
Octahedral
*Count the bonding and nonbonding PAIRS of electrons around the central atom ONLY
# In the case of double or triple bonds, count them as ONE PAIR