Experiment 14-VSEPR Model Lab
Introduction
In this lab you will be examining covalently bonded structures called molecules. On paper these
molecules look very different from their true three-dimensional structures. In this lab we will
practice drawing two-dimensional Lewis structures on paper and then look at these structures
transformed into three dimensions using the model sets provided in the laboratory. You will
then draw the molecules using three-dimensional drawing techniques. The models sets contain
balls with holes that represent atoms and sticks that connect them that represent bonds.
OCTET RULE-Atoms in a compound lose, gain or share electrons in order to achieve a stable
noble gas configuration. Not all elements follow this rule, but most do. Hydrogen in a sense
follows this rule because its electron configuration is that of an inert gas. Atoms that do not
follow this rule in any form will always be noted in this lab.
(NOTE: IF YOU GET LOST IN THIS LAB TRY LOOKING AT THIS TUTORIAL WEBSITE)
Prelab Questions (Answer in complete sentences!)
1. What does each letter in the VSEPR theory stand for and what can it be used to predict and how?
2. At the subatomic level, what do the holes in the balls represent?
3. Why does the ball representing nitrogen in some model kits have three holes and others four?
4. Why does the ball representing sulfur in some model kits have two holes and others six?
5. Draw the Lewis structures for NO and NO2. (These are an exception to the “octet rule”)
6. What is the hybridization, the molecular geometry and the bond angle of the molecule from question
number 5?
7. What exception to the octet rule do elements of period 2 show and why?
8. What exception to the octet rule do elements of period 3 and higher show and why?
Part I: Exploring the Shapes of Molecules Model Set.
1. Make models of each of theses structures HCl, CH4, NH3, H2O, CCl4, CH2F2, SF6, PCl5 and draw pictures
of these (VSEPR diagram) along with the Lewis dot structure. Name the hybridization around the
central atom. Name the molecular geometry of each of these molecules. Note the bond angles around
the central atom. Then predict which of these molecules are dipoles and indicate the polarity of that
molecule in your report. (Hint: Molecular polarity is based on bond polarity and molecular shape!)
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Part II: Exploring the Inorganic Molecule Model Set.
1. Make models of each of theses structures H2, O2, N2, CO2, SO2, SO3, CH2O and draw pictures of these
(VSEPR diagram) along with the Lewis dot structure. Name the hybridization around the central
atom. Name the molecular geometry of each of these molecules. Note the bond angles around the
central atom. Then predict which of these molecules are dipoles and indicate the polarity of that
molecule in your report. (Hint: Molecular polarity is based on bond polarity and molecular shape!)
2. Polyatomic ions are groups of covalently bound groups of atoms with an overall charge. Draw all
(Hint: resonance structures are possible!) Lewis dot structures for the ions CO32-, CHO2-, NO3- and
NO2-. Make models of each. Draw a three-dimensional picture of each polyatomic ion (VSEPR
diagram). Name the hybridization and the molecular geometry of each polyatomic ion. Note the bond
angles around the central atom.
Part III: Exploring the Organic Teacher Model Set. (In this section you do not have to do Lewis
Structures, unless you want them to aid you in making the models)
1. Make a model for C2H6. Notice that the carbons spin freely around the single bond like a helicopter.
Draw a VSEPR diagram. Name the hybridization, bond angle, and the molecular geometry for the
carbon atoms.
2. Make a model for C2H4. Notice that the carbons do not spin freely around the double bond. Draw a VSEPR
diagram. Name the hybridization, bond angle, and the molecular geometry for the carbon atoms.
3. Now make the model for C2H2 for ethyne (more commonly called acetylene) and draw a VSEPR diagram. Name
the hybridization, bond angle, and the molecular geometry for the carbon atoms.
4. Now make the models for C4H8 for butene. Notice that the double bond does not spin around. In fact,
you can make this molecule in three different ways. With the double bond between the two middle
carbons there are two geometric isomers. The molecule with the CH3's on the same side of the double
bond is called cis and the molecule with the CH3's on the opposite side of the double bond is called
trans. Please draw the cis and trans isomers of this compound. A third molecule (structural isomer) is
possible by moving the double bond to be between the first and second carbon. Write down all VSEPR
diagrams for all three structural/geometric isomers. Identify the molecular geometry, hybridization and
bond angles around each carbon atom.
5. Now make a model of ethanol, C2H5OH and draw a VSEPR diagram. Name the hybridization, bond
angle, and the molecular geometry around the carbon atoms and around the oxygen atom. Identify the
nonpolar end and polar end of this molecule.
6. There is another possible molecule that has the same molecular formula as ethanol, C2H6O (or
CH3OCH3), make this model and draw a VSEPR diagram. Name the hybridization, bond angle, and the
molecular geometry around the carbon atoms and around the oxygen atom. Identify the nonpolar end
and polar end of this molecule.
7. Now make two models of propanol, C3H7-OH and draw a VSEPR diagram of each. Name the
hybridization, bond angle, and the molecular geometry around the carbon atoms and around the oxygen
atom. Identify the nonpolar end and polar end of these molecules.
8. Now make a model of ethanoic acid, CH3COOH and draw a VSEPR diagram. Name the hybridization,
bond angle, and the molecular geometry around the carbon atoms and around the oxygen atom with a
hydrogen attached. Identify the nonpolar end and polar end of this molecule. A resonance structure is
possible when a hydrogen atom is lost of the oxygen atom, so make it and then draw a VSEPR diagram
9. Now make a model of a two ring compounds, C6H6 and C6H12 draw a VSEPR diagram of each. Name
the hybridization, bond angle, and the molecular geometry around one of the carbon atoms in each of the
models.
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Post-Lab Questions
1. What shape would VSEPR predict for xenon tetrafluoride? What hybridization is shown by the
molecule? (Hints: Make a Lewis electron dot structure for the molecule and it will not follow the octet
rule!)
2. H2S and H2O have similar VSEPR models, but hydrogen sulfide is a gas at room temperature and water
is a liquid. What accounts for this difference in their physical properties?
3. What kinds of hybridizations, molecular geometry and bond angles are possible around a carbon atom?
4. How would you show bonding between calcium ion and chloride ions? Hint: This is not like what you
have been doing!
5. How is it possible to have polar bonds within a molecule, but yet the molecule is nonpolar? Use
examples from this lab to explain your answer.
6. The two molecules made in Part III, procedures 5 and 6, have two different boiling points. Dimethyl
ether has a boiling point of 34.5oC and ethanol has a boiling point of 78.4oC, explain the different
boiling points even thought the two molecules have the same molecular formula.
7. The two molecules made in Part III, procedure 7, have two different boiling points. 1-proponol has a
boiling point of 97oC and 2-proponol has a boiling point of 82oC, explain the different boiling points
even thought the two molecules have the same molecular formula.
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Experiment 14: VSEPR Lab
Grading Protocol
Name: ________________________
Item
Name & Partner
Date Experiment Started
Title of Experiment
Appropriate Purpose
Appropriate Procedure
Procedure Initialed
Prelab Questions
Part I
Part II
Part III
Post Lab Questions
Signature
TOTAL
Points/Out of
/1
/1
/1
/1
/1
/1
/19
/24
/34
/29
/22
/1
/135
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