« Return to AACT homepage

AACT Member-Only Content

You have to be an AACT member to access this content, but good news: anyone can join!


Need Help?

Intermolecular Forces (30 Favorites)

SIMULATION in Intermolecular Forces, Physical Change, Intermolecular Forces. Last updated June 22, 2017.


Summary

In this activity, students will use a simulation designed by the Next-Generation Molecular Workbench to investigate different types of intermolecular forces (London dispersion and dipole-dipole). In the analysis that follows the activity, they will relate IMFs (including hydrogen bonding) to physical properties (boiling point and solubility).

Grade Level

High school

Objectives

By the end of this lesson, students should be able to

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

Chemistry Topics

This lesson 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:

o Intermolecular forces (IMFs)
o Electronegativity
o Polarity
o How physical properties relate to IMFs

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 by 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 bonds, dipole-dipole interactions, induced dipole attraction, and London dispersion forces.

Procedure

  1. Visit the comparing attractive forces simulation.
  2. From the dropdown menu “select a pair of molecules” choose “pull apart Br2 and Br2.”
  3. Predict how difficult it will be to pull apart the two molecules in the data table.
  4. Using the green star, move one Br2 away from the other. Comment on how easy or difficult this was in the data table.
  5. From the dropdown menu, choose “pull apart H2 and H2.”
  6. Predict how difficult it will be to pull apart the two molecules in the data table.
  7. Using the green star, move one H2 away from the other. Comment on how easy or difficult this was in the data table.
  8. From the dropdown menu, choose “pull apart HBr and HBr.”
  9. Predict how difficult it will be to pull apart the two molecules in the data table.
  10. Using the green star, move one HBr away from the other. Comment on how easy or difficult this was in the data table.
  11. From the dropdown menu, choose “pull apart Br2 and HBr.”
  12. Predict how difficult it will be to pull apart the two molecules in the data table.
  13. Using the green star, move Br2 away from HBr. Comment on how easy or difficult this was in the data table.

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
Br2 & Br2
H2 & H2
HBr & HBr

Br2 & HBr

Analysis

  1. Explain why you classified the intermolecular forces the way you did for each pair of molecules taking into account polarity.
    1. Br2 & Br2
    2. H2 & H2
    3. HBr & HBr
    4. Br2 & HBr
  2. 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.
  3. If HF was used in the simulation instead of HBr, 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:
Data
Molecules Predict Polar/nonpolar? IMF
Br2 & Br2

HF & HF

Br2 & HF

Explain your IMF classifications, taking into account polarity.

  1. How would you expect HF’s boiling point to compare to HBr? Explain. You can use the Molecular Workbench simulation Boiling Point to help you.
  2. If F2 was used in the simulation instead of Br2, 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:
Data
Molecules Predict Polar/nonpolar? IMF

F2 & F2

HBr & HBr

F2 & HBr

Explain your IMF classifications, taking into account 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. Look up the boiling points of H2O, Br2, F2, HBr, and HF. Were your predictions correct? Explain.
  5. Of the two original compounds you investigated in the simulation (HBr and Br2), which would be soluble in water? Explain.
  6. 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.