Lab: Shapes of Molecules
FOR THE TEACHER
Summary
In this lab, students will investigate the VSEPR geometry of covalent compounds. They will draw
Lewis structures, use molecular models, and determine the geometry of covalent compounds.
There is a lot of repetition so students gain a lot of practice.
Resource Type
Lab
Grade Level
High school
Objectives
By the end of this lesson, students should be able to
 Recognize from a Lewis structure the molecular geometry of a compound.
 Understand VSEPR theory.
Chemistry Topics
This lesson supports students’ understanding of
 Molecules and bonding
 VSEPR theory
 Molecular geometry
 Resonance
 Covalent bonding
Time
Teacher Preparation: 10 minutes
Lesson: 1 class period and complete for homework
Materials
For each group:
 A set of molecular models
Safety
No safety considerations need to be observed for this investigation.
Teacher Notes
 It’s helpful to have samples of each geometry at the front of the class so students can
familiarize themselves with how to assemble molecular models.
o Tetrahedral (four atoms around one central atom)
o Trigonal pyramidal (three atoms, one unbonded pair of electrons around one
central atom)
o Trigonal planar (three atoms and no unbonded electrons around one central
atom)
o Bent (two atoms and two pairs of unbonded electrons around one central atom)
o Linear (two atoms and no unbonded electrons around one central atom)
 This investigation only covers compounds that satisfy the octet rule. A possible extension
could be to add more complicated molecules that extend past the octet rule.
FOR THE STUDENT
Student Activity Sheet: Shapes of Molecules
Lesson
Background
The valence shell electron pair repulsion (VSEPR) theory is how the geometry of a
molecule is determined. It’s called “vesper” theory for short. The shapes that are
possible are tetrahedral, trigonal planar, trigonal pyramidal, bent, and linear. To
determine the shape of a molecule, you must look at the central atom. Unbonded
electrons around the central are not accounted for in the geometry, however they
are important because they determine the geometry. Unbonded electrons around
atoms that are not the central atom have little effect on the geometry.
In this experiment, you will draw Lewis structures for a number of
compounds and use them to determine how the molecular models need to be
assembled. From the models, you will determine the geometry of the compounds.
After completing a few examples, you should start to see how the two dimensional
drawings really exist in three dimensions.
Procedure
Complete each column in order. Compare your model to the samples at the front of
the room if you are confused about which geometry your model makes.
Molecule
Lewis structure
Lewis structure with
VSEPR
Total
(write the
(check the box if a
proper geometry
geometry
valence
chemical
resonance structure is
(use the models to
(the name of
eformula)
possible)
help here)
the shape)
Water
Nitrogen
Carbonate
Sulfite
Carbon
tetrachloride
Ammonium
Bromine
Carbon
monoxide
Dinitrogen
monoxide
Ozone
Nitrate
Nitrite
Bromate
Chlorite
Phosphate
Acetic Acid
(try your
best! Both
carbons are
in the
middle.)
Analysis
Without using the models, determine the geometry of these compounds (you can
draw Lewis structures to help you):
NF3
F2
SO3 (not sulfite!)
H2S
SO2
OCl2
SO42-
HCN
ClO3-
Conclusion
All of the compounds in this exercise are what kind of compound? Explain why this
is important.