VSEPR Web Exercise
Go to www.chem.purdue.edu/gchelp/vsepr. The first page on this site defines VSEPR. Links on the left side of the page
take you through rules for determining VSEPR structures and exercises that apply those rules.
This exercise will help you explore this site, learn VSEPR concepts and apply them. You and your partner will work on
this exercise in class today and turn it part of it either before leaving today or on Friday. Please save your work as a
google doc so that I can grade it. You will email this to me through a gmail account.
Part I: Getting Started – Answer the following questions in the provided spaces.
a) What does VSEPR stand for?
b) What can we use the VSEPR model for? (list two uses)
Part II: VSEPR Rules – Now click on the link entitled “Rules” and answer the following questions.
c)
Write out Rules 1 & 2 below:
1.
2.
d) Which of the following count as ONE region of electron density? Circle all that apply.
Bonding pairs? Unshared pairs? Double bonds? triple bonds?
e) Now click on the Examples link to view illustrations of Rule #2.
1. Which example(s) listed below illustrates 2 regions of electron density? Circle your choice(s).
HCN
CH4
BF3
NH3
CO2
PCl5
2. Which example(s) illustrates 3 regions of electron density? Circle your choice(s).
HCN
CH4
BF3
NH3
CO2
PCl5
CO2
PCl5
3. Which illustrates 4 regions of electron density? Circle!
HCN
CH4
BF3
NH3
4. Which illustrates 5 regions of electron density? You know what to do!
HCN
CH4
BF3
NH3
CO2
PCl5
f) Then return to the previous back and click on the Test My Knowledge link.
g) Complete the following numbered practice problems. Fill in the table with the requested information
Practice
Problem
Lewis Structure (draw it)
# of Regions of Electron Density Around Central
Atom listed according to
Bonded
Unshared pairs
pairs
1
8
3
h) Return to the “Rules” page and write out Rule #3 below:
3.
Part III: Arranging Regions of Electron Density – Click on the link that takes you to the page describing how to arrange
regions of electron density around your central atom. The listed arrangements are also referred to as electron group
geometries.
i)
Use the information on this page to fill in the table below. Click on the names of each arrangement to view
diagrams of the arrangements.
# of Regions of
Electron Density
Best Arrangement
Drawing showing arrangement of electron groups
(including bond angle)
2
3
4
5
6
j)
Which of the arrangements are planar, i.e., all groups in the same plane? List them below.
k)
Which of the arrangements are 3-D? List them below.
l)
Now return to the Rules page and write out #4 & #5 below:
4)
5)
Part IV: Molecular Structures bases on VSEPR Theory: Click on the link to view molecular structures based on VSEPR.
These are structures that you arrive at by 1st determining the best arrangement of electron density regions and then
choosing a shape based on the arrangement of the bonded regions.
For an example, find NO2- on this page. This molecule has 3 regions of electron density, so we arrange those in a
trigonal planar arrangement. Only two of the three regions are bonded, so the molecular structure or shape is bent.
Use the information on this page to fill in the table below. After turning in this last page, you will get a handout from
your instructor that summarizes this information for you to include in your class notes. Keep the rest of this exercise as
part of your notes as well.
Name
s
Computer #
m) Fill in the table below with the requested information. Note that not every box will be filled in for every electron
group geometry listed. Include the bond angles where you can for the molecular geometries. Turn in one copy
of ONLY this page per pair.
# of Regions of
Electron Density
aka Electron
Group Geometry
2
3
4
5
Molecular
Structure for
Molecular
Structure for
Molecular
Structure for
Molecular
Structure for
Molecular
Structure for
0 unshared pairs
1 unshared pairs
2 unshared pairs
3 unshared pairs
4 unshared pairs
6