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UNIT 3 DAY 5
Intermolecular Forces
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 nowAnswer 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?
Period 1 Period 5 Period 7 Period 2 Period 4 Period 6 Period 865
70
75
80
85
90
73
8782
7581 82
Unit 3 Day 4: Ionic Bonds Class Average Mastery
Announcements
Edmodo – see class codes on boardACT tutoring Sat 9am-12pmBehavior Grade every two weeks - loginOffice hours: Tuesday, Wednesday and
ThursdayNew homework policy – NO late work
acceptedBRING YOUR NOTES PACKET EVERYDAY!
Homework Due Exam Unit 3Friday 11/9 ODD Wednesday 11/14
ODDTuesday 11/13 EVEN
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. Dispersion Forces2. Dipole-Dipole Forces3. Hydrogen Bonding
Dispersion Forces
Result from interactions between molecules, temporary charges between non-polar molecules. They are very weak.
Results from Strength Diagram
Attractive force between neighboring molecules, caused by motion of electrons
Weakest of all the forces
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 Diagram
Negative region of one polar molecule attracted to positive region of other polar molecule
Medium strength
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 Diagram
Slightly positive H bonded to one atom is also weakly attracted to another EN atom
ONLY N, O, F or Cl
Strongest of the forces
Hydrogen Bonding: Diagram
We Do: CFU #1
Order these forces from strongest to weakest: Hydrogen Bonding, Dispersion Forces, Dipole-Dipole Interactions, Covalent Bonds.
Covalent bonds, hydrogen bonding, dipole-dipole 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):Definition2 factsOne 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?