Yakima WATERS Mini Lesson
Intermolecular forces
Targets and Assessment
WA Science Standards Addressed:
9-12
Feedback is a process in which the output of a
SYSA system provides information used to regulate
the operation of the system. Positive feedback
increases the disturbance to a system. Negative
feedback reduces the disturbance to a system.
9-12
SYSC
In complex systems, entirely new and
unpredictable properties may emerge.
Consequently, modeling a complex system in
sufficient detail to make reliable predictions
may not be possible.
9-11
PS2H
Solutions are mixtures in which particles of one
substance are evenly distributed through
another substance. Liquids are limited in the
amount of dissolved solid or gas that they can
contain. Aqueous solutions can be described by
relative quantities of the dissolved substances
and acidity or alkalinity (pH).
The rate of a physical or chemical change may
be affected by factors such as temperature,
surface area, and pressure
Assessments:
 Intermolecular Forces Formative/Summative
Assessment
Lesson Parameters
Content Area: Chemistry
Overview: In this lesson student will learn about
intermolecular forces and their effects on chemical
properties.
Grade Level: 11th&12th grader
9-11
PS2I
Suggested Time: 45 to 55 minutes
Special Materials:
 See materials section
Author: Sara Rosario, Yakima WATERS Project, CWU, Fall 2010
Learning Outcomes:
Knowledge: Upon completion of this lesson students should know the three types of intermolecular
forces, the difference between intermolecular and intramolecular forces, and how intermolecular
forces determine the state of a substance at room temperature, boiling points, vaporization
temperatures, surface tension and solubility.
Skill: Students should be able determine the type of intermolecular forces that occur between
molecules, determine a molecule’s polarizability, estimate boiling points, vaporization temperature
and solubility.
Science Concept Background:
Intermolecular forces are the relatively weak attractions and repulsions between molecules; this
should not be confused with intramolecular forces which are the attractions between atoms in the
same molecule despite their similarities. These forces act over a relatively large distance typically Van
Der Waals radii or larger. Intermolecular forces are largely dependent on the charge density and
location (in laymen’s term the location of electrons in a molecule). At the molecular level charge
density of a molecule is the result of atomic radius, affective nuclear charge, electron configuration and
electronegativity of the atoms in the molecule. There are three main types (or four depending on the
text book you’re using) of intermolecular forces. 1) Dipole-Dipole, 2) London dispersion (AKA Van der
Waals forces) and 3) Hydrogen Bonding. Dipole –Dipole forces are the attractive force occurs between
neutral polar molecules. London Dispersion forces are the attractive force occuring between all
molecules but it is the main attractive force between nonpolar covalent molecules. Hydrogen bonding
is a special type of dipole-dipole force the occurs only between hydrogens bonded to the either
nitrogen, oxygen or fluorine and the unpaired electrons on oxygen (O), nitrogen (N) and sometimes
Fluorine (F) of a neighboring molecule. Hydrogen bonding is the strongest intermolecular force
followed by dipole-dipole and London dispersions forces. The strength of these forces depends on the
following conditions: distance between molecules, orientation of molecules and location of molecules
within a liquid or solid. The state of matter, properties such as boiling point vaporization temperature
and colligative properties depend on the balance of the average kinetic molecules in the system and
the attractive forces at work in the system. In general molecules that have weak intermolecular forces
are gases at room temperature; liquids have slightly stronger intermolecular forces while solids have
the strongest intermolecular forces. This is readily apparent in the molecular structure of the states of
matter. For a substance to change states the kinetic energy of the system needs to be increased until
molecules are able to escape each other’s attractive forces. As the strength of the intermolecular
forces increase the boiling point and vaporization temperature increases.
Materials:
- Density Column Demo Materials (see attached). Prepare enough of each liquid for two density
column
- Intermolecular Forces formative assessment & Intermolecular Forces Summative assessment (see
attached), two per students
- Paperclip floating activity materials (see attached).
- Intermolecular forces lecture power point.
Procedure:
1) Set up density column demonstration in a location that is easily accessible for 20 or more students.
If this is not possible then set up two or three density columns in different locations. Handout
Intermolecular forces formative assessment. Allow students about 5 or 10 minutes to make
observations and predictions. Mix the density column by inverting a few times, give students an
additional 5 or 10 minutes to finish the assessment. Collect the formative assessment and quickly
read through responses to the last question and be sure to follow up on misconceptions.
2) Give Intermolecular forces lecture, stop at the first hydrogen bonding slide to do paperclip floating
activity. This activity should take about 10 minutes.
3) Finish intermolecular forces lecture, but stop before metacognition activity.
4) Set up another density column and handout Intermolecular summative assessment (this is the
same as the Intermolecular force formative assessment). Give students about 20 minutes to
complete the assessment.
5) Collect the summative assessment. At this point explain the density column demo. Be sure to tell
students which layers mixed with each other and why.
6) Now do metacognition activity. Collect metacognition activity the following class period.
Extension(s):
This lesson can be extend to include colligative properties such as lowering of vapor pressure, elevation
of boiling point ordepression of freezing point and osmotic pressure. Or this lesson can be extend to include
an in-depth discussion of waters unique properties.
Teaching Tips:
For this lesson to be effective student need to have a firm understanding of polarity, dipole moments,
electron distribution in molecules, and the periodic trends for electronegativity, atomic radius and affective
nuclear charge. Students should also be able to differentiate between ionic, polar covalent and nonpolar
molecules. Make sure you practice the density column demo before doing it in class.
Supplements:
Intermolecular Force Formative/Summative Assessment
Instructions: In the front of the room you will find a graduate cylinder in which there are five layered liquids,
listed in order from top to bottom there is methanol, Glycerol, KBr, Mineral Oil and Water. Make a few
observations (with our eyes and not our hands) of the liquid layers in the graduated cylinder (Hint: It may be
helpful to note the number of layers, what is in each layer and where that layer is located before and after
mixing). Then make predicts about the quantity, location and combination of the liquid layers after mixing.
After the liquid layers get mixed make a few more observation and answer the following questions
Observations:
Predictions:
Which liquids mixed?
Why did the layers mix the way they did? Propose an explanation for why some of the liquids were soluble with
each other (meaning the liquids mixed) while others were not.
Paperclip Floating Activity
Materials:
- 10 or 15 Petri dishes (depending on class size, but 10 Petri dishes is enough for a class of 20 to 25
students)
- 50 to 100 mL of deionized water
- 50 to 100 mL of 50/50 methanol & water
- 100 paperclips
Directions:
Place about 10 mL of water in to five Petri dishes and 10 mL of methanol into five Petri dishes (it may
be helpful to do this ahead of time so that you can make the best use of class time), there is no need to tell
students which Petri dishes have water or methanol they will quickly figure that out. Place Petri dishes in a
location that is easily accessible for large groups of students, place paperclip near petri dishes. Have students
try to float the paperclips on the liquids, tell them to gently place the paperclip on the surface of the liquid.
Ask to student to write a four or five sentence explanation as to why paperclips will not float on methanol. Ask
a few students to share their hypotheses with the class. Most students will use surface tension to explain why
the paperclip does not float on water. Use surface tension to lead into a lecture on hydrogen bonding.
Density Column Demo
Materials:
- Two 100 mL graduated cylinders
- 50 mL of 40% KBr in water with green food coloring
- 50 mL of methanol with red food coloring
- 50 mL mineral oil no food coloring
- 50 mL water with blue food coloring
- 50 mL glycerol no food coloring
Directions:
In one of the 100 mL graduated cylinders place 15 to 20 mL of each liquid in the following order KBr,
glycerol, water, mineral oil and methanol. When adding liquids to the graduated cylinder be sure not to mix
the liquids. To do this tilt the graduated cylinder and slowly pour each liquid.