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.