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Molecular Structures
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Objectives
• To determine the number of valence electrons in molecules.
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To determine the Lewis structure of molecules.
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To determine the electron pair geometry and geometry (shape) of molecules.
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To determine the hybridization of molecules.
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To build molecular models.
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To draw three-dimensional picture of models.
In the Lab
• Students will work in pairs.
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You do not need to write a full lab report for this experiment.
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Complete the Chem21 worksheet assignment.
Waste
•None
Safety
• Students need to wear goggles for this experiment.
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 E x p e r i m e n t
1 1 • Molecular Structures
A team of researchers looking into developing new drugs
are using molecular modeling to see how the new drugs
fit into the cell’s receptors for this drug. Molecular modeling uses mathematical models to describe molecular
properties and behaviors of molecules and generally
displays that information in the form of a picture. Before
the researchers can build their mathematical models,
they need you to help provide some information about
the basic structures of some simple molecules.
Expt.
11
Materials
Molecular model set with the following parts
16 sp3 (black)
10 sp2 (gray)
2 half double bond (blue)
4 double bond (purple)
4 octahedral (metallic gold)
For each of the molecules in the lists below, use your
model kit to construct a model of the compounds and to
provide the researchers with the following information:
2 linear (orange)
2 trigonal (copper)
1 triple bond (yellow)
Total number of electrons:
2 bond extenders (silver)
1. Valence electrons
2. Bonding electrons
3. Non-bonding electrons
marker balls
Number of bonds—single, double, triple
Hybridization
12 white (hydrogen)
6 green (halogens)
6 red (oxygen and nitrogen)
2 hot pink (undesignated atoms)
Number of electron groups
Electron geometry
Model Sets
Molecular geometry
3-D drawing of molecule
These model sets are from Darling Models (http://
www.darlingmodels.com). Sets similar to this one
and many others are available at a very reasonable price
if you are interested in having your own set or if you
will be taking Organic Chemistry. Most Organic Chemistry courses will require or recommend that you have
a model set.
All information needs to be provided to your supervisor
through the Chem21 website, so that it can easily be
converted into the mathematical models. Your TA will
tell you which list you should report on.
Your supervisor has provided the following instructions
in regards to using the molecular model kits available
to you.
Assembly and Disassembly of Molecular
Visions™ Atoms
Darling Models™; pieces shown in Figure 11.1.
Figure 11.1. From top to bottom, sp3 piece, trigonal
atoms, octahedral pieces, and linear bond.
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E x p e r i m e n t
1 1 • Molecular Structures The tetrahedron may be taken apart by gently spreading
the “V” shaped bonds on one piece, to unlock the teeth,
while pushing it out of its locked position.
The Atom
Figure 11.2. The “U” shaped center of the atom piece.
Each atom consists of a “U” shaped center as shown in
Figure 11.2, with two or three “bonds.” The bonds end
in a rod or tube. The small teeth at the opening of the
“U” serve to grip the square at the end of the other piece,
locking the two pieces to form an atom “with bonds.”
The procedure for joining two atom pieces is shown in
the following paragraphs.
This may be accomplished in one motion with one hand,
by placing two or four fingers across the “V” of one
piece and the ball of the thumb on the opposite side. A
gentle squeeze will spread the “V” slightly and push the
two pieces apart. In Figure 11.5, the left hand stabilizes
the piece while the right hand spreads both pieces and
separates them.
Expt.
The Tetrahedral Atom
Figure 11.3. Assembling the tetrahedral atom
“with bonds.”
1.
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11
Figure 11.5. Disassembling the tetrahedral atom.
The Trigonal-Bipyramid Atom
Slide the “U” openings together at right angles (see
image above).
2. Pinch the two pieces together until they click (see
image below).
3. Grasp the two pieces against the central “U.” Pull
sharply with the left hand and push sharply with
the right hand until there is a second click as shown
in Figure 11.4.
Figure 11.4. The final step to assemble the tetrahedral
Figure 11.6. Assembly of a trigonal bipyramid.
Figure 11.7. Disassembly of a trigonal bipyramid.
atom “with bonds.”
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1 1 • Molecular Structures
A linear bond is joined at right angles with a trigonal
atom using the same push-pull motion as for the tetrahedral atom.
Creating Bonds between Atoms
Bonds are formed between atoms by joining the rod of
one atom with the tube of another. The pieces should be
gripped firmly as shown to prevent bending of the rod.
The trigonal bipyramid is disassembled by slightly spreading the opening of the trigonal atom with the thumbs
while using the two fingers of the right hand to pull the
linear bond towards the user.
The Octahedral Atom
Figure 11.10. Creating bonds between atoms.
Instructions courtesy of Darling Models™, P.O. Box
1818, Stow, OH 44224 or on the web at
www.darlingmodels.com.
Expt.
11
Figure 11.8. Assembly of an octahedral atom.
The octahedral atom is assembled by pushing the two
octahedral pieces together.
The octahedral atom is disassembled by placing two fingers of each hand around the horizontal bonds of each
respective piece and gently pulling the pieces apart as
shown in Figure 11.9.
Figure 11.9. Disassembly of the octahedral atom.
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Electron Groups
Electron groups are any electron cloud that acts to repel
another group of electrons. This would include single,
double, triple bonds as well as lone pairs. The idea of
an electron group or cloud is at the heart of the VSEPR
model describing the repulsive interactions that result
from coulombic forces within atoms. How much of a
repulsive force occurs determines the geometry of the
molecule (Table 11.1).
Hybridization
When atoms come together to form molecules, the orbitals found within the atom are not the same as they
were when they were a single atom. Hybridization is the
mathematical way in which the changes in the shapes
and energies of orbitals are described and occurs most
frequently with atoms in the interior of molecules. The
type of hybridization that occurs depends on the number
of available orbitals participating in the bonding, such
that the number of atomic orbitals that goes in equals
the number of degenerate hybrid orbitals that come out.
E x p e r i m e n t
1 1 • Molecular Structures 
Table 11.1. VSEPR geometry.
# of
e– Groups
e– Pair Geometry
# of
Lone Pairs
Molecular Geometry
Ideal Bond Angles
2
linear
0
linear
180°
3
trigonal planar
0
trigonal planar
120°
3
trigonal planar
1
bent
120°
4
tetrahedral
0
tetrahedral
109.5°
4
tetrahedral
1
trigonal pyramid
109.5°
4
tetrahedral
2
bent
109.5°
5
trigonal bipyramidal
0
trigonal bipyramidal
90°, 120°, 180°
5
trigonal bipyramidal
1
seesaw
90°, 120°, 180°
5
trigonal bipyramidal
2
t-shaped
90°, 180°
5
trigonal bipyramidal
3
linear
180°
6
octahedral
0
octahedral
90°
6
octahedral
1
square pyramidal
90°
6
octahedral
2
square planar
90°
Drawing Molecules in 3-D
Use the model you build to help you draw a 3-D drawing
of the molecule. Rotate the molecule so that as many
bonds and/or lone pairs as possible are in the same plane.
Draw this portion of the molecule. Without moving the
model, look for bonds projecting out of the plane. Any
bonds projected toward you should be indicated with a
solid wedge and bonds projected away from you should
be drawn with a dashed triangle. See example for water
molecule shown on page 56. The lone pairs are in the
Expt.
11
plane, while one O–H bond projects toward you and
the other O–H bond is projecting out of the plane away
from you.
Multiple Central Atoms
For molecules with more than one central atom, give
the electron pair geometry and geometry (shape) around
each central atom. Mark the information for each atom
so that it is apparent which information goes with which
atom. See the second example for more information.
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1 1 • Molecular Structures
Table 11.2. List of molecules.
Expt.
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List 1
List 2
List 3
List 4
1
CCl4
NH4+
PO43–
CF4
2
PCl5
NO
NO
CO2
3
SO32–
PBr5
SbF5
CH3Cl
4
CO
PCl
IF3
AsI5
2–
3
–
2
–
6
–
3
5
ICl2–
ICl3
ICl2+
BrF5
6
CHCH
CH2CH2
NH2NH2
C2O42–
7
CH3CH2CH2OH
CH3CH2OCH3 (O is
bonded to two carbons)
CH3CH2CHO
CH2CHOCH3 (O is
bonded to two carbons)
8
CH3CH2CN
CH2CHCH2Cl
CH3CH2COO–
CH3CH2NH2
9
SF6
XeF2
SeF4
SF2
10
XeF4
ClO3–
PCl3
PF3
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C6H6 (all carbons in the
ring, don’t forget resonance structures)
O3 (center O, don’t forget
resonance structures)
C6F6 (all carbons in the
ring, don’t forget resonance structures)
O=CN (don’t forget
resonance structures)
12
C7H14
(all carbons in the ring)
C4H8
(all carbons in the ring)
C5H10
(all carbons in the ring)
C6H6
(all carbons in the ring)
–
E x p e r i m e n t
1 1 • Molecular Structures 
For you and your lab partner to work on the same computer, you will need to have two different browsers open. For
example, you would need to log onto Chem21 using Internet Explorer while your lab partner logged onto Chem21
using Chrome or Firefox.
You and your lab partner MUST enter the same List Number so that you are working on the same list of molecules.
Compound 1: CH3CHCH2
Number of Electrons
Valence
Electrons
Bonding
Electrons
NonBonding
Electrons
Number of Bonds
Points
Single
Double
Triple
Points
Hybridization /Geometry
Electron Groups
Hybridization
Electron Geometry
Molecular Geometry
Expt.
3D Drawing
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 E x p e r i m e n t
1 1 • Molecular Structures
Examples
Compound 1: H2O
Number of Electrons
Valence
Electrons
Bonding
Electrons
NonBonding
Electrons
8
4
4
Number of Bonds
Points
Single
Double
Triple
2
0
0
Points
Hybridization /Geometry
Electron Groups
Hybridization
4
sp
Electron Geometry
Molecular Geometry
tetrahedral
bent
3
3D Drawing
Expt.
11
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E x p e r i m e n t
1 1 • Molecular Structures 
Compound 2: CH3CHCH2
Number of Electrons
Valence
Electrons
Bonding
Electrons
NonBonding
Electrons
18
8
0
Number of Bonds
Points
Single
Double
Triple
7
1
0
Points
Hybridization /Geometry
Electron Groups
Hybridization
3
sp
Electron Geometry
Molecular Geometry
trigonal planar
trigonal planar
2
3D Drawing
Expt.
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Expt.
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1 1 • Molecular Structures