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 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)

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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 Forces 2. Dipole-Dipole Forces 3. Hydrogen Bonding

Dispersion Forces Result from interactions between molecules, temporary charges between non-polar molecules. They are very weak. Results fromStrengthDiagram 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 fromStrengthDiagram 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 fromStrengthDiagram 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 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?