Intermolecular Forces
UNIT 3 DAY 5
Do Now/Catalyst (8 min)
Entrance Slip: Write your name and period at the top.
 If you did not do Day 2, Day 3 or Day 4 Questions, do those
now
 Answer the questions under Day 5.
 You may use your notes.
 SHOW:
 Calculation
to find the number of bonds (2
pts)
 Correct Lewis Structure (2 pts)
How are you doing?
Unit 3 Day 4: Ionic Bonds Class Average Mastery
90
85
80
87
75
70
82
81
82
75
73
65
Period 1
Period 5
Period 7
Period 2
Period 4
Period 6
Period 8
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 BRING
YOUR Due
NOTES PACKET
Homework
ExamEVERYDAY!
Unit 3
Friday 11/9 ODD
Tuesday 11/13 EVEN
Wednesday 11/14 ODD
Thursday 11/15 EVEN
Objectives: Intermolecular Forces
 SWBAT define Van der Waals,
Dispersion, Dipole-Dipole, and
Hydrogen Bonding forces and
compare their relative strengths.
Real World!
Water Striders can
walk on water
because of
hydrogen bonding
and strong
attractions in the
water molecules!
Intermolecular Forces
 Intermolecular Forces are forces between
individual atoms or compounds that hold
molecules together. They are weaker than
the bonds between atoms in a molecule,
which are called intramolecular forces.
 Reminder: dipole results from differences in
electronegativity, which produce small
charges on atoms in a molecule.
Intermolecular Forces
 Intermolecular forces come in three types,
depending on polarity.
1.
2.
3.
Dispersion Forces
Dipole-Dipole Forces
Hydrogen Bonding
Dispersion Forces
 Result from interactions between molecules,
temporary charges between non-polar molecules.
They are very weak.
Results from
Strength
Attractive force Weakest of
between
all the forces
neighboring
molecules,
caused by
motion of
electrons
Diagram
Dispersion Forces: Diagram
Dipole-Dipole Interactions
 Result from permanent partial charges. These
forces are also polar, and thus slightly stronger
than dispersion forces.
 Note:
Both Dispersion Forces and Dipole-Dipole
Interactions are sometimes called van der waals forces.
Results from
Strength
Negative region of
one polar molecule
attracted to positive
region of other polar
molecule
Medium
strength
Diagram
Dipole-Dipole Interactions: Diagram
Hydrogen Bonding
 Very similar to intramolecular forces. These are
strong and permanent forces (“bonds”) that
result from a special type of polar attraction.
Form between H and either N, O, F or Cl ONLY.
Results from
Strength
Slightly positive H
bonded to one atom
is also weakly
attracted to another
EN atom
Strongest
of the
forces
ONLY N, O, F or Cl
Diagram
Hydrogen Bonding: Diagram
We Do: CFU #1
Order these forces from strongest to weakest:
Hydrogen Bonding, Dispersion Forces, DipoleDipole Interactions, Covalent Bonds.
Covalent bonds, hydrogen bonding, dipoledipole interactions, dispersion forces
We Do: CFU #2
True or False: Intermolecular Forces hold the
atoms in a molecule together
False
We Do: CFU #3
True or False: These forces rely on differences in
polarity, which produces small charges on the
molecules.
True
We Do: CFU #4
Do you think it would be harder to pull a molecule
away from a compound that was held together using
Hydrogen Bonds or Dipole-Dipole Interactions? Why?
 Hydrogen bonds, they have stronger
interactions
We Do: CFU #5
Do forces get stronger or weaker as differences in
electronegativity increase (as polarity increases)?
Stronger
You Do: Forces Poster (20 min)
Fold paper into 3 sections, one for dipole
interactions, dispersion forces and hydrogen
bonding. On your posters include the
following information for each force (use
notes and p.250-51 of text):
 Definition
 2 facts
 One real world example (except for Dipole)
 Drawing/diagram
Chemistry Interim Test
 Counts as a grade so do your best!
 Mark all answers on your answer sheet
 25 questions
Closing
Essential Question:
 What holds the individual molecules in a
compound together?