Lecture 4.2 – Intermolecular Forces
and the Dissolving Process
Today’s Learning Targets
• LT 4.1 – I can discuss how ionic solids dissolve due to the
random molecular motion of the water molecules.
• LT 4.2 – I can identify a compound as containing
hydrogen bonding, dipole – dipole forces, and Van der
Waals forces.
• LT 4.3 – I can compare and contrast various
intermolecular forces and relate them to the dissolving
process of a solid.
Watch Mr. Astor Cook Pepperonis
• Why do pepperoni pizzas taste so
delicious?
• What substance is creating the taste?
Explanation for Deliciousness
• Fats are basically long carbon chains, and how well they
pack at low temperatures is determined by how long they
are and how many kinks they have in the chain from C=C
double bonds. Liquid fats (like oils) have lots of kinks (also
called unsaturations) that prevent it from packing tightly
when cold, so they stay liquid.
• When you cook pepperoni, these fats are effectively
rendered - they melt, dissolving out some of the colour and
flavour compounds from the meat and spices. The fat acts
as a nonpolar organic solvent, drawing out some nonpolar
compounds in the meat you may find delicious. Lots of
flavorful substances dissolve in fat better than in water, like
capcaisin (from chili peppers) and cinnamic acid (from
cinnamon).
What are intermolecular forces?
I. Intermolecular Forces
• Intermolecular forces are forces that attract molecules
to one another.
• The three main types of intermolecular forces are:
(1) Hydrogen Bonding
(2) Dipole-Dipole Forces
(3) Dispersion Force (also known as Van der Waals
Forces)
H
δ+
This is
what a
dipole
looks like
Pulls electrons
towards itself
because it has a
higher
electronegativity
F
δ-
H F
Partial negative
charge
III. Dipole-Dipole Forces
• Dipole-dipole forces refer to the attraction
between molecules that have a permanent
dipole.
What Dipole-Dipoles Look Like
Partial negative attracted to
the partial positive
III. Dispersion Forces
• Some molecules have an induced dipole.
• Dispersion forces are the intermolecular
forces resulting from the uneven distribution
of electrons and the creation of temporary
dipoles.
• Weakest intermolecular force
But, when two H2
molecules are put next
to one another, a
dipole is induced
because electrons
rearrange themselves
There is no
electronegativity
difference between
two hydrogens, so
they are non-polar and
do not have a dipole
What the Heck?
IV. Hydrogen Bonding
• Hydrogen bonding is the attraction of one molecule
that contains hydrogen to another molecule.
• When hydrogen is bound to N, O, or F, there is a large
difference in electronegativity
• Creates a partial positive and negative charge
• The partial positive charge on hydrogen is attracted
to N, O, or F of another molecule.
Hydrogen
bond
between H
and O
V. Intermolecular Forces and Phase of
Substance
• The degree of intermolecular forces determines
the phase of a substance.
Least
intermolecular
forces
Most
intermolecular
forces
SUMMARIZE
White Board Races
White Board Race Questions
• Draw what atoms in a solid state look like. What
type of movement do they have?
• What state has the least intermolecular forces?
• What type of bonds does solution of HF have?
• C12H24 has no permanent dipoles, what type of
intermolecular forces does it have?
White Board Races
• HCl looks like this:
δ+
δ-
H Cl
• What type of intermolecular forces exist in a solution
of HCl?
• What is the strongest intermolecular force?
Let’s talk Wikispace
• Units 1, 2, and 3 need to be finished to completion.
• This means every lesson from Units 1, 2, and 3
must have a video, script, and picture.
• Unit 3 must have all of the Kool-Aid Molarity Lab
including the excel graph portion!
• Need help with microsoft excel? Check out this
“Microsoft Excel and Chemistry” document.
Microsoft Excel and Chemistry
Lab Report!
Lab Report!
You will be writing a formal lab report on the lab
“Lab 6 – What is the Concentration of Kool Aid”.
This lab report will be divided into four sections:
• Introduction
• Materials and Procedures
• Results
• Discussion
Introduction Section
• Contains:
– 1 paragraph providing background information for
the lab (what are the LARGE chemistry concepts
covered?)
– 1 paragraph stating the purpose of the lab and
how it ties into the background
– 1 sentence hypothesis in an “If ______, then
______ because ___________” format
• Make sure to write in 3rd person
Discussion Section
• Contains:
– 1 paragraph regarding the conclusions you drew
from the lab
– 1 paragraph per post-lab question
– 1 paragraph discussing sources of error:
• Human error: Error from your inaccuracy
• Experimental error: Problems with lab design
• Make sure to write in 3rd person
Closing Time
• Homework 4.1
• Wikispaces
• Formal Lab Report