« 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?

VSEPR with Balloons (8 Favorites)

ACTIVITY in Covalent Bonding, VSEPR Theory, Molecular Geometry, Lewis Structures. Last updated August 17, 2019.


Summary

In this activity, students will explore Valence Shell Electron Pair Repulsion Theory using balloon models. Since balloons tend to take up as much space as they can when tied together, they can look like models of central atoms in VSEPR theory, making a great metaphor for the model. This activity is an extension of the activity, Shapes of Molecules found on the AACT website.

Grade Level

High School

NGSS Alignment

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

  • HS-PS1-1: Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.
  • 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 1: Atomic Structure and Properties
    • Topic 1.5: Atomic Structure and Electron Configuration
      • SAP-1.A: Represent the electron configuration of an element or ions of an element using the Aufbau principle.
  • 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 2.2: Intramolecular Force and Potential Energy
      • SAP-3.B: Represent the relationship between potential energy and distance between atoms, based on factors that influence the interaction strength.
    • Topic 2.5: Lewis Diagrams
      • SAP-4.A: Represent a molecule with a Lewis diagram.
    • Topic 2.6: Resonance and Formal Charge
      • SAP-4.B: Represent a molecule with a Lewis diagram that accounts for resonance between equivalent structures or that uses formal charge to select between nonequivalent structures.
    • 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

Objectives

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

  • Define the VSEPR theory and explain its relationship to the shape of molecules.
  • Differentiate electron pair geometry from molecular geometry.
  • Name and describe the five electron pair geometries which can surround the central atom.
  • Use balloons to illustrate the different electron pair geometries around the central atom.
  • Show how molecular geometry is a function of electron pair geometry.
  • State the two factors that determine the polarity of a molecule.
  • Explain how the geometry of a molecule helps to determine its properties.
  • Organize their information in the form of a chart.

Chemistry Topics

This activity supports students’ understanding of

  • Valence Shell Electron Pair Repulsion Theory
  • Lewis Structures
  • Valence Electrons
  • Molecular Geometry
  • Polarity

Time

Teacher Preparation: 10 – 15 minutes

Lesson: 45 – 60 minutes

Materials

  • Student Handout
  • Balloons for each group:
    • ~12 colored balloons
    • 4 white balloons
  • Extras balloon (for popped balloons)
  • String or rubber bands (can be helpful for tying balloons together)
  • Colored pencils

Safety

  • If you are using latex balloons, check to see if any students have latex allergies/sensitivities.

Teacher Notes

  • I have used this lesson with AP Chemistry classes, college-prep Chemistry II, and college-prep Chemistry I. It may need to be slightly modified for lower level classes, especially if Lewis structures are difficult for them. However, the visual focus of this activity does seem to help many of my students grasp the concept of shapes of molecules.
  • Groups of 2-4 students is recommended.
  • This activity should follow a full lesson on Lewis Structures, including exceptions to the octet rule. Although the students start out by drawing Lewis Structures, those specific molecules are not the only shapes that the students will build.
  • This activity is an extension of the activity, Shapes of Molecules found on the AACT website.
  • In the directions, the students are guided to blow up the balloons as big as possible. This is so that the balloons fill as much space as possible and more accurately represent VSEPR models. This also will result in fragile balloons popping. The activity is loud and can be scary, since balloons will pop throughout the lesson at random times. It is best to let nearby classrooms know that you are doing this activity!
  • Do not fear the popped balloons. It is a really important part of the lab activity. It helps to make the experience memorable for the students. I like to celebrate popped balloons with my students by saying that they were clearly trying to make the most accurate models possible. This can be tricky though, as you probably do not have an infinite supply of balloons. I usually try to ration the amount of balloons per group and only provide enough for a few popped balloons.
  • The directions state this, but invariably some students will not follow the directions. It is helpful if the students go through the activity with the colored balloons, tying them all together with no lone pairs before moving on to how lone pairs of electrons affect the geometry of the molecule. You also will need to remind the students that they cannot “see” the white balloons (or whatever color you choose to represent the lone pairs), but they can see the effect that the white balloons have on the shape of the molecule.
  • A VSEPR Geometry chart is available to be printed and given to students as a modification (chart originally accessed from Wikimedia). This will change the data table from matching words to 3D models to matching 2D models to 3D models. As an additional option, you could also could also print out this page, cut up the pieces, and then let the students glue these images instead of drawing them.

For the Student

Lesson

Background

In this activity, you will explore the Valence Shell Electron Pair Repulsion Theory for covalent bonding. This theory is a way for us to visualize the shapes of molecules. It is important for you to be able to draw Lewis Structures for molecules in order to successfully create a VSEPR model.

Prior Knowledge

  1. Before you begin the activity, please define the following terms:
    1. Coulomb’s Law:
    2. Electronegativity:
    3. Polar Covalent Bond:
    4. Nonpolar Covalent Bond:
    5. Polar molecule:
    6. Nonpolar molecule:
    7. Bonding electron domain:
    8. Non-Bonding electron domain:
    9. Electron domain geometry:
    10. Molecular geometry:
  2. Draw Lewis Structures for the following molecules:

BeH2

BH3

CH4

SO2

NH3

H2O

PCl5

SF6

Materials

  • Colored balloons (to represent the bonding electron domains)
  • White balloons (to represent the lone pair electrons)
  • String/Rubber bands
  • Colored pencils, for drawing different types of electron domains

Safety

  • Please inform your instructor if you have a latex allergy/sensitivity.

Procedure

  1. Pick a color for your bonding domain balloons. Blow up the balloons as large as you can and tie it together to another balloon. Place the balloons as far apart as possible from each other. Draw a representation of the balloons in the first row of the data table.
  2. Add another colored balloon, so that there are 3 balloons tied together. Draw a picture of them on the second row of the data table.
  3. Keep adding colored balloons and draw pictures of each structure that results, as described/moving down the data table.
  4. Describe the shape of each of the pictures. Use the following Molecular Geometry vocabulary as a word bank to name the shapes:
    1. Linear
    2. Trigonal Planar
    3. Tetrahedral
    4. Trigonal Bipyramidal
    5. Octahedral.
  5. Make new models by inserting different combinations of white balloon(s) to represent a lone pair of electrons. Draw new pictures, moving down the data table, using a lighter color for the lone-pair balloons.
  6. Describe the shape of each of the new pictures, disregarding the lone-pair electrons in the shape you describe, since lone pair electrons cannot be seen. Use the following Molecular Geometry vocabulary as a word bank to name the shapes:
    1. Bent
    2. Trigonal Pyramidal
    3. Square Pyramidal
    4. Square Planar
    5. T-Shaped
    6. See-Saw
    7. Linear

*Vocabulary words can be used more than once.

Results

Total electron pairs around the central atom

Number of bonding domains

Number of Lone Pairs around the central atom

Illustration

Molecular Geometry

Molecular Geometry Vocabulary: Linear, Trigonal Planar, Tetrahedral, Trigonal Bipyramidal, and Octahedral

2

2

0

3

3

0

4

4

0

5

5

0

6

6

0

Total electron pairs around the central atom

Number of bonding domains

Number of Lone Pairs around the central atom

Illustration

Molecular Geometry

Molecular Geometry Vocabulary:
Bent, Trigonal Pyramidal, Square Pyramidal, Square Planar, T-Shaped, See-Saw, Linear

3

2

1

4

3

1

4

2

2

5

4

1

5

3

2

5

2

3

6

5

1

6

4

2

6

3

3

6

4

2

Analysis

Answer the following questions, using the pictures of your models and the vocabulary from the background section and the Pre-Lab activity.

  1. What is an electron domain?
  2. In this model, single bonds, double bonds, and triple bonds take up the same amount of space. Compare and contrast the validity of that assumption. What aspects are accurate and what aspects are in conflict with Coulomb’s Law?
  3. The basic idea of VSEPR theory is that electron pairs repel each other as much as possible. Is this in line with Coulomb’s Law? Describe how?
  4. What is the difference between electron domain geometry and molecular geometry?
  5. Describe how electron domain geometry and molecular geometry can affect the overall polarity of a molecule. You may use an example in your response, like BF3 and NF3, for example.

Conclusion

Choose any 2 of the following questions. Answer each question and then connect your responses to each other in a cohesive paragraph.

  • Can a molecule with polar bonds be considered nonpolar overall?
  • How do lone pair electrons affect the polarity of a molecule?
  • How does this activity relate to visualizing molecules in three dimensions?
  • How does the molecular geometry of a central atom relate to a multi-centered molecule, like C2H6?