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VSEPR Lab Activities

Instructor: Heather Jenkins

Heather has a bachelor's degree in elementary education and a master's degree in special education. She was a public school teacher and administrator for 11 years.

As students explore the VSEPR theory, they may need some hands-on experiences to help them understand different electron pair geometries. Use these lab activities to help students apply the VSEPR theory to common molecules.

The Geometry of Molecules

Most students probably never stop to think about the world around them constantly makes order out of chaos. Even the smallest molecules of water or carbon dioxide are arranged in a specific way. When students learn about the valence shell electron pair repulsion (VSEPR) theory, they can begin to understand the unseen way elements in a molecule organize themselves. Students can also use the presence of high concentrations of electrons in different parts of a molecule to predict how it will be shaped. Let's look at some lab activities to help students understand and apply the VSEPR theory.

Balloon Models

Have students use balloons to create the electron pair geometries based on the VSEPR theory.

Materials

  • Diagrams of electron pair geometries
  • Oblong/pear-shaped balloons
  • Tape

Teacher Directions

  1. Discuss the possible electron pair geometries for molecules based on the VSEPR theory, such as linear, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral.
  2. Show students diagrams of the different molecular shapes, and provide examples of molecules that have each type of shape.
  3. Divide the class into pairs, and provide each pair with balloons and tape.
  4. Have students create models of the electron pair geometries using the balloons and tape. Students can twist balloons together to create the different shapes or use tape to help hold the balloons together.
  5. When students are finished, have them share their creations with the class.

Discussion Questions

  • How did you and your partner go about making the models of the electron pair geometries?
  • What determines the shape of a molecule?

Gum Drops and Toothpicks

Students will create candy models of common molecules and find the bond angles.

Materials

  • Diagrams of electron pair geometries
  • Gum drops
  • Toothpicks
  • Protractors
  • Index cards

Teacher Directions

Preparation

  1. Prior to the activity, write the chemical formula of common molecules, such as water and sodium nitrate, that represent different electron pair geometries on index cards (one formula per card).
  2. On each index card, write the electron pair geometry for the chemical formula.

Activity

  1. Show student diagrams of electron pair geometries for molecules based on the VSEPR theory. Discuss the expected bond angles for each configuration.
  2. Divide students in pairs, and provide each pair with gum drops, toothpicks, a protractor, and one of the index cards you created.
  3. Students will use the information on the index card to create a gum drop and toothpick model of the molecule's electron pair geometry. Encourage students to use different colored gum drops to represent the elements present in each molecule.
  4. When students have constructed their models, have them use their protractors to measure the angles of the bonds created in the molecule. Students should compare their measurements to the expected measurements for the configuration of the molecule.
  5. Pairs should trade index cards with their classmates after they are finished and create another model for a different molecule.
  6. Repeat the process until students have created at least several models of molecules and measured their bond angles.

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