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Simulation Activity: Comparing Attractive Forces Mark as Favorite (109 Favorites)

ACTIVITY in Physical Properties, Intermolecular Forces, Polarity, Molecular Motion, Molecular Motion, Intermolecular Forces. Last updated July 25, 2023.

Summary

In this activity, students will use a simulation to investigate different types of intermolecular forces (London dispersion, induced dipole, and hydrogen bonding). In the analysis that follows the activity, they will relate IMFs (also including dipole-dipole) to physical properties (boiling point, solubility, and vapor pressure). This activity and simulation are appropriate for students in any level chemistry course.

Grade Level

High School

NGSS Alignment

This activity will help prepare your students to meet the performance expectations in the following standards:

  • HS-PS1-3: Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.
  • Scientific and Engineering Practices:
    • Developing and Using Models
    • Analyzing and Interpreting Data

AP Chemistry Curriculum Framework

This activity supports the following units, topics and learning objectives:

  • Unit 2: Molecular and Ionic Compound Structure and Properties
    • Topic 2.1: Types of Chemical Bonds
      • SAP-3.A: Explain the relationship between the type of bonding and the properties of the elements participating in the bond.
    • Topic 2.7: VSEPR and Bond Hybridization
      • SAP-4.C: Based on the relationship between Lewis diagrams, VSEPR theory, bond orders, and bond polarities:
        • Explain structural properties of molecules.
        • Explain electron properties of molecules.
  • Unit 3: Intermolecular Forces and Properties
    • Topic 3.1: Intermolecular Forces
      • SAP-5.A: Explain the relationship between the chemical structures of molecules and the relative strength of their intermolecular forces when:
        • The molecules are of the same chemical species.
        • The molecules are of two different chemical species.

Objectives

By the end of this activity, students should be able to:

  • Better understand the relative strengths of intermolecular forces.
  • Relate intermolecular forces to physical properties

Chemistry Topics

This activity supports students’ understanding of:

  • Intermolecular forces
  • Physical properties

Time

Teacher Preparation: 10 minutes

Lesson: 30 minutes

Materials

  • Computer with internet connection

Safety

  • No specific safety precautions need to be observed for this activity.

Teacher Notes

  • This lesson is most effective if students have some prior knowledge about the following:
    • Intermolecular forces (IMFs)
    • Electronegativity
    • Polarity
    • How physical properties relate to IMFs
  • Don’t be intimidated by the AP Chemistry learning objectives listed above – this resource can be used for any level high school chemistry students! There may be a few questions in the Analysis section that might be more challenging for less advanced students, but those could either be removed or discussed as a class.
  • To introduce the general concept of dipole-dipole forces vs. London dispersion forces, you can use the Molecular Workbench simulation called Comparing Dipole-Dipole to London Dispersion.
  • To further investigate hydrogen bonding, you can use the Molecular Workbench simulation called Hydrogen Bonds: A Special Type of Attraction. There are many more related chemistry simulations available from The Concord Consortium as well!
  • Note that the simulation used in this activity was updated in Fall 2022. It originally used Br2, HBr, and H2, but now includes F2, HF, and H2 instead. The student worksheet has been updated to reflect this change, so if you used this resource in the past you may want to look at the updated student document and answer key.
  • Students will likely be a bit surprised when they look up the boiling points for question 8 and find that Br2 has a higher boiling point than both HBr and HF. Many of the questions on the student handout could lead to good discussions between students, including question 8 and the conclusion question. It may benefit students to talk about these questions with a partner before answering them on paper.
  • The AACT Classroom Resource Library includes many more resources to help students understand intermolecular forces! Here are a few of the most popular:

For the Student

Lesson

Background

Compounds interact with each other differently depending on their polarity. These interactions are called intermolecular forces (IMFs), and physical properties of compounds can be inferred based on the type of IMFs. In this activity, you will have the opportunity to “feel” the strength of different intermolecular forces with the help of a computer simulation, and then you will consider what that means about some of the compounds’ physical properties. Remember, the IMFs are hydrogen bonding, dipole-dipole interactions, induced dipole attractions, and London dispersion forces.

Procedure

  1. Visit the simulation Comparing Attractive Forces: https://teachchemistry.org/classroom-resources/comparing-attractive-forces-simulation.
  2. From the dropdown menu “Select a pair of molecules,” choose “Pull apart H2 and H2.”
  3. Predict how difficult it will be to pull apart the two molecules in the data table.
  4. Using the green star, move one H2 away from the other. Comment on how easy or difficult this was in the data table.
  5. From the dropdown menu, choose “Pull apart F2 and F2.”
  6. Predict how difficult it will be to pull apart the two molecules in the data table.
  7. Using the green star, move one F2 away from the other. Comment on how easy or difficult this was in the data table.
  8. From the dropdown menu, choose “Pull apart HF and HF.”
  9. Predict how difficult it will be to pull apart the two molecules in the data table.
  10. Using the green star, move one HF away from the other. Comment on how easy or difficult this was in the data table.
  11. From the dropdown menu, choose “Pull apart H2 and HF.”
  12. Predict how difficult it will be to pull apart the two molecules in the data table.
  13. Using the green star, move HF away from H2. Comment on how easy or difficult this was in the data table.
  14. In the last two columns, determine whether the molecules are polar or nonpolar and identify the type of intermolecular forces the molecules exhibit.

Data

Molecules Predict Actual Polar/nonpolar? IMF
H2 & H2
F2 & F2
HF & HF

H2 & HF

Analysis

  1. Explain why you classified the intermolecular forces the way you did for each pair of molecules, considering polarity.
    1. F2 & F2
    2. H2 & H2
    3. HF & HF
    4. H2 & HF
  1. If HBr was used in the simulation instead of HF, how easy or difficult would it be to separate the molecules? What kind of polarity and IMFs would the molecules experience? Complete the following data table with your predictions:
Molecules Predict Polar/nonpolar? IMF
F2 & F2

HBr & HBr

F2 & HBr

Explain your IMF classifications, considering polarity.

  1. How would you expect HBr’s boiling point to compare to HF’s? Explain. Use the Molecular Workbench simulation Boiling Point (http://bit.ly/1xEty5j) to help you.
  2. If Br2 was used in the simulation instead of F2, how easy or difficult would it be to separate the molecules? What kind of polarity and IMFs would the molecules experience? Complete the following data table with your predictions:
Molecules Predict Polar/nonpolar? IMF

Br2 & Br2

HF & HF

Br2 & HF

Explain your IMF classifications, considering polarity.

  1. How would you expect F2’s boiling point to compare to Br2? Explain.
  2. How would you expect HBr’s boiling point to compare to Br2? Explain.
  3. Consider the familiar compound, water (H2O). How would water’s boiling point compare to HBr and HF? Explain.
  4. Using your answers to the previous questions, predict the order of the following molecules from lowest boiling point to highest: H2O, Br2, F2, HBr, and HF. Then look up their actual boiling points. Were your predictions correct? Explain.
  5. If you had samples of HBr(aq) and Br2(l) in real life and you mixed them together, would you expect them to mix or separate into two layers? Explain.
  6. Which compound, HBr or Br2, would you expect to be soluble in water? Explain.
  7. Rank the vapor pressures of water, HBr, and HF from lowest to highest. Explain.

Conclusion

When considering physical properties, are IMFs the only factor to consider? Explain.