Experiment 11 - Molecular Geometry
PRE-LABORATORY ASSIGNMENT
Name________________________________________
1. Draw the Lewis structures for the following molecules:
a. AlF3
b. SiBr4
c. AsF3
d. TeO22+
e. GaH4
Section _________
Use the Lewis structures from page 106 in order to answer the questions:
2. What is the molecular geometry of an AX3E2 molecule?
__________________
3. Number of lone e- pairs on As in AsF3
__________________
4. Hybridization of As in AsF3
__________________
5. In problem #1, which of the molecules are polar?
__________________
6. In problem #1, which molecules have polar bonds?
__________________
7. Total number of valence electrons for XeO3
__________________
8. Arrangement of electrons for AsF3
__________________
9. Molecular geometry of SiBr4
__________________
10. Number of  bonds in TeO22+
__________________
11. Number of  bonds in TeO22+
__________________
12. Molecular geometry of AsF3
__________________
13. Hybridization of Si in SiBr4
__________________
14. Which atom is the central atom in AlO2?
__________________
15. Number of orbitals hybridized in sp3d hybridization
__________________
16. Bond angle between the atoms in TeO22+
__________________
Experiment 11 - Molecular Geometry
INTRODUCTION
Note: Most of the technical information about Lewis structures, formal charge, geometry,
polarity and hybridization can be found in your general chemistry textbook.
Drawing Lewis structures:
It is very important to be able to draw Lewis structures. A properly drawn Lewis structure will
assist in determining the correct molecular geometry, hybridization, VSEPR formula, and
polarity of the compound.
Steps to drawing the Lewis structure:
1. Select the central atom. The central atom is usually the least electronegative element in the
formula (the exceptions are hydrogen or fluorine will can not bet the central element).
2. Connect the "outside" atoms to the central atom by using single (2 e) bonds. Each bond is
represented by a straight line or 2 dots.
3. Determine the total number of valence electrons by summing the number of valence
electrons for each of the atoms in the molecule.
4. For anions, add electrons equal to the magnitude of the charge of the ion and for cations,
subtract electrons equal to the magnitude of the charge on the cation.
5. Subtract the electrons used in step 2 from the total in step 3. Distribute the remaining
electrons. Place electrons until each of the "outside" atoms have 8 electrons around them.
6. If there are valence electrons left over, the extra electrons are put around the central atom as
unbonded electrons (also called lone pairs). The central atom may have more than 8
electrons around it if it is in the 3rd period (Al, Si, P, S, Cl) or lower. Alternately, if the
central element is in group III (or 13) it may have fewer than eight electron around it.
7. If the central atom has fewer than 8 electrons around it (and does not fall into the exceptions
listed in step 6), then you need to use unbonded electrons from the outside atoms to make a
double bond between that outside atom and the central atom. This will ensure that the
outside atom still has 8 electrons around it and also gives the central atom 2 more electrons.
8. The Lewis structure can then be checked using the rules for formal charge. The rules for
calculating and evaluating formal charges can be found in your textbook or lecture notes.
Assigning a VSEPR formula (AXE formula):
Note: The "AXE" notation is defined as
A = The central atom
X = Number of atoms directly attached to the central atom
E = Number of lone electron pairs on the central atom
For example: AX2E means there is one lone electron pair on the central atom and 2 (two) atoms
directly attached to the central atom. It does not matter whether they are attached using single,
double, or triple bonds.
Assigning Polarity
For a detailed discussion on assigning polarity please refer to your textbook or lecture notes.
PROCEDURE
From the list below, your laboratory instructor will assign a number of molecules for you to
draw. For each of the molecules, you need to do the following:
1.
2.
3.
4.
5.
6.
7.
Draw the Lewis structure
Determine the VSEPR formula for the molecule
Determine the number of  bonds and  bonds in the molecule
Determine the geometry of the molecule
Determine the hybridization on the central atom
Determine the polarity (polar / nonpolar) of the molecule
Draw a 3-dimensional sketch of the molecule
Here is the list of molecules:
1. BeF2
2. BF3
3. SO2
4. SO3
5. SO426. NO27. NO38. CO329. NH4+
10. CH2Cl2
11. KrF2
12. TeO2
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
CS2
SF4
SF6
AsCl52IF2I3BrF3
SiH4
SnCl2
CH3SeO3
XeF4
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
ICl4+
PCl4+
H3O+
O3
NO2+
GeF4
AlCl3
CF4
XeF2
PN2PON
PO33-
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
SiF62BrF5
SnF62XeO64SbF4ClO3H2O
SnF4
AlO2CH3+
BO2HCN
Total
Regions
2
VSEPR
Formula
AX2
Bonding
Regions
2
AX3
3
Nonbonding
Hybridization
Regions
0
sp
0
3
sp
AX2E
AX4
2
4
2
1
Geometric
Shape
Linear
Trigional
Planar
V-shaped
0
Tetrahedral
4
sp3
Trigonal
Pyramidal
AX3E
3
1
AX2E2
2
2
Bent
0
Trigonal
Bipyramidal
AX5
AX4E
5
4
Unsymmetrical
Tetrahedron
1
3-D Shape
AX3E2
3
2
*
A
*
A
*
*
*
*
*
*
*
A
*
*
A
*
*
A
*
*
*
A
*
*
*
*
*
A
*
sp3d
5
A
*
*
*
A
T-shaped
*
*
*
AX2E3
2
3
*
A
Linear
*
AX6
6
0
Octahedral
sp3d2
6
AX5E
5
1
Square
Pyramid
AX4E2
4
2
Square Planar
*
*
A
*
*
*
*
*
*
A
*
*
*
*
*
A
*
*
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Experiment 11 - Molecular Geometry
REPORT
Name________________________________________
Section _________
Lewis structure
3-D sketch
Lewis structure
3-D sketch
Molecule
AXE
 bonds
 bonds
Geometry
Hybridization
Polarity
Molecule
AXE
 bonds
 bonds
Geometry
Hybridization
Polarity
Lewis structure
3-D sketch
Lewis structure
3-D sketch
Lewis structure
3-D sketch
Molecule
AXE
 bonds
 bonds
Geometry
Hybridization
Polarity
Molecule
(and number)
AXE
 bonds
 bonds
Geometry
Hybridization
Polarity
Molecule
(and number)
AXE
 bonds
 bonds
Geometry
Hybridization
Polarity
Lewis structure
3-D sketch
Lewis structure
3-D sketch
Lewis structure
3-D sketch
Molecule
AXE
 bonds
 bonds
Geometry
Hybridization
Polarity
Molecule
(and number)
AXE
 bonds
 bonds
Geometry
Hybridization
Polarity
Molecule
(and number)
AXE
 bonds
 bonds
Geometry
Hybridization
Polarity
Lewis structure
3-D sketch
Lewis structure
3-D sketch
Lewis structure
3-D sketch
Molecule
AXE
 bonds
 bonds
Geometry
Hybridization
Polarity
Molecule
(and number)
AXE
 bonds
 bonds
Geometry
Hybridization
Polarity
Molecule
(and number)
AXE
 bonds
 bonds
Geometry
Hybridization
Polarity
Lewis structure
3-D sketch
Lewis structure
3-D sketch
Lewis structure
3-D sketch
Molecule
AXE
 bonds
 bonds
Geometry
Hybridization
Polarity
Molecule
(and number)
AXE
 bonds
 bonds
Geometry
Hybridization
Polarity
Molecule
(and number)
AXE
 bonds
 bonds
Geometry
Hybridization
Polarity
POST-LABORATORY QUESTIONS
1. Using your textbook, determine the bond angle for the first three molecules in your
assignment.
2. Draw the two possible structures for AX3E2 and determine the preferred structure.
Briefly justify your answer.