Concept Presentation
By:
Amarinder Sawhney
Jeffrey Ip
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Why does salt dissolve in water?
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Water is a polar molecule: one end has a
slightly positive charge, another has a
slightly negative charge
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When the NaCl crystals get closer to the
positively and negatively charged poles of
the H2O molecule, the Na+ and Cl- ions are
pulled apart
You can think of the H2O molecule as a
strong magnet
Click here for more details
Attraction between (polar) water molecules
and ions is an example of intermolecular
forces at work (specifically ion-dipole
forces)
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Intermolecular forces are the forces of attraction
and repulsion between molecules. Intermolecular
forces should not be confused with intramolecular
forces, which are the electrostatic forces that hold
the atoms of a molecule together (e.g., covalent
and ionic bonds)
Intermolecular forces are typically weaker than
intramolecular forces, and account for the bulk
properties of matter (e.g., boiling point, melting
point, etc.)
Intermolecular forces are also known as van der
Waals forces, named after Johannes van der Waals
who first postulated them
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Dispersion (London)
Dipole-induced dipole
Ion-induced dipole
Dipole-dipole
Hydrogen bond
Ion-dipole
http://www.chem.ufl.edu/~itl/4411/lect
ures/lec_g.html
Periodic Trends – students will learn about the periodic table, the different
groups of elements, and the how atomic radius, electronegativity, etc.,
change across rows and columns. (B2.1, B2.2, B3.3)
Electronegativity – students will learn to predict the nature of a bond (e.g.,
nonpolar covalent, polar covalent, ionic), using electronegativity values of
atoms. (B2.1, B2.5)
Intramolecular Forces – Students will explore the difference between ionic
and covalent bonds and their formation. (B2.1, B3.4)
Lewis Structures and Molecular Models – Students will learn to draw Lewis
structures to represent bonds in ionic and molecular compounds.
Students will also build molecular models and write structural formulae to
familiarize themselves with the shape and structure of molecules. (B2.1,
B2.4, B2.6).
Intermolecular Forces – Students will learn about intermolecular forces
through lecture, a jigsaw activity, an inquiry based online module, and a
lab
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Video demonstration can be viewed here
http://workbench.concord.org/database/ac
tivities/227.html
This is a two day module that allows
students to explore intermolecular forces
concepts in greater detail using an
interactive inquiry based online module
Once completed students will “Create a
Report of [their] Work” and hand it in for
marking
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This jigsaw activity is a cooperative learning activity where
students collaborate to explore concepts related to intermolecular
forces
Instructions: Students form groups of (number of people per
group depends on class size). Members of the group are
numbered off. Each number is assigned a type of intermolecular
force (e.g. Hydrogen bonding, dipole-dipole, etc.). Students with
the same number form a new group (an “expert group”) and
research on their assigned intermolecular force. Once research is
complete, students reform their original groups and take turns
teaching each other about their assigned intermolecular force.
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Students will complete a graphic organizer
(e.g. Flow chart, concept map, mind map,
etc.) to summarize and demonstrate the
knowledge they have gained about
intermolecular forces so far
This will be used as a formative assessment
Click here for an example
Penny drop experiment
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Found here on pg. 35 – 37
NOTE: a selection of 6 labs are found in the same document
for teachers to choose from (pg. 27 and following)
This lab addresses the relationship between surface tension
and strength of intermolecular forces, so prior to lab the
concept of surface tension should be reviewed
Students place droplets of water on a penny until it spills over
and they note the number of droplets
Students place droplets of rubbing alcohol on a penny until it
spills over and they note the number of droplets
They record their observations and answer discussion
questions related to intermolecular forces
Safety
 Rubbing alcohol is used in this lab and it is
both toxic and flammable, so students should
be warned not to ingest it or let fire near it
Assessment
 Students write up a lab report in standard
format including observation chart, answers to
discussion questions, discussion of sources of
error, and a conclusion; they are assessed
based on KICA criteria
Role of intermolecular forces
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• The granulated sugar falls essentially grain by grain off of the black contact
paper into
the sugar container and all of the sugar falls off (a few grains may remain).
This is due
to the force of gravity on the sugar particles.
• The powdered sugar falls off in one clump. There will be a trail left by the
powdered
sugar as well as clumps of powdered sugar remaining on the card. Even if the
card is
tipped upside down, these clumps will remain on the card. All of this is due to
electrostatic forces, specifically Van der Waals forces, and not gravity.
• The size of the object affects the dominant forces acting upon it.
• IMPORTANT: The powdered sugar is not nanosized! The average particle
size is 1-10
μm, which is 1,000-10,000 times bigger than a nanometer.
Role of intermolecular forces in illustrating behaviour of ZnO
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• Zinc oxide forms weakly agglomerated nanoparticles.
• An aqueous dispersion of zinc oxide is very viscous due to Van der Waals
interactions
which in turn makes the liquid very difficult to stir.
• Addition of Darvan C, a polyelectrolyte, coats each nanoparticle with negative
charge.
This causes the particles to repel each other significantly lowering the viscosity.
• This repulsion causes the particles no longer want to stick together as much and
the
solution becomes easy to stir.
• The behavior of the ZnO illustrates how important electrostatic forces are in
determining the behavior of the ZnO solution.
• The ZnO particles range from 200-800 nm which is much closer to the
nanometer size
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1. Why oil and water don’t mix?
2. What is role of hydrogen bonding in DNA
model?
3. What role is played by intermolecular
forces in human immune system?
http://workbench.concord.org/database/ac
tivities/227.html
All application answers are in this link
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Maintaining appropriate internet conduct
Students will be given explicit instructions to
perform jigsaw activity and role play
effectively
Proper use of PPE in penny drop lab
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Diagnostic assessment (after demonstration): Exit ticket, and/or
KWL chart [K/U, C]
Jigsaw activity: Students fill out an information chart covering all
concepts that expert groups research; informal observations by
teacher [K/U, T/I, C]
Interactive online module: Students hand a printed copy of their
work by clicking the “generate report” button on the module and
hand it in to be marked [K/U, T/I, C, A]
Graphic organizer: Students hand in their completed graphic
organizer for marks [K/U, T/I, C]
Students complete problem sets for homework [K/U, T/I]
Students write a test/ quiz about the material [K/U, T/I, C, A]
NOTE: K/U = knowledge and understanding, T/I = thinking and
investigation, C = communication, and A = application
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Visual – Spatial and Kinesthetic learners may have difficulties
understanding the 3-D shapes of the atoms, valence electrons
and orbitals as well as the shapes of the molecules. Hence, the
shape and the bonding properties would be difficult to
determine. This could be addressed by using hands-on
laboratories and role playing of bonds and atoms.
Students will have difficulties with abstract ideas and therefore
need to view videos, demonstrations.
Special needs and students with exceptionalities must be
accommodated to fit their varying learning styles and modified
according to their individual IEPs. (lab activities)
A handout for ELL learners will be given. A sample handout
with important terms is given in the next slide.
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SCH3U
B3. demonstrate an understanding of periodic trends in the periodic table and how elements combine to form
chemical bonds
B2.1 use appropriate terminology related to chemical trends and chemical bonding, including, but not limited
to: atomic radius, effective nuclear charge, electronegativity, ionization energy, and electron affinity
B2.2 draw Lewis structures to represent the bonds in ionic and molecular compounds
B2.5 predict the nature of a bond (e.g., non-polar covalent, polar covalent, ionic), using electronegativity
values of atoms
B2.6 build molecular models, and write structural formulae, for molecular compounds, including those with
multiple valences, and name the compounds using the IUPAC nomenclature system
B3.3 state the periodic law, and explain how patterns in the electron arrangement and forces in atoms result in
periodic trends (e.g., in atomic radius, ionization energy, electron affinity, electronegativity) in the periodic
table
B3.5 compare and contrase the physical properties of ionic and molecular compounds (e.g., NaCl and CH4;
NaOH and H2O)
E3.1 describe the properties of water (e.g., polarity, hydrogen bonding), and explain why these properties make
water such a good solvent
E3.2 explain the process of formation for solutions that are produced by dissolving ionic and molecular
compounds (e.g. Salt, oxygen) in water, and for solutions that are produced by dissolving non-polar solutes in
non-polar solvents (e.g., grease in vegetable oil)
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Salt and Water demonstration:
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf
Good overview of intermolecular forces concepts:
http://www.chem.ufl.edu/~itl/2045/lectures/lec_g.html
Inquiry based online module for intermolecualr forces:
http://workbench.concord.org/database/activities/227.html
Sample graphic organizer:
http://www.concord.org/~btinker/molo/molo_concept_maps/atom_forces_attractions.html
Intermolecular forces labs (including the Penny Drop Lab plus other activities and a concept
overview):
http://www.haspi.org/curriculumlibrary/MedicalChemistry/03%20Standard%202%20Chemical%20Bonds/Labs%20and%20Activitie
s/IntermolecularForces.pdf