Molecular Geometry with Balloons

Background

Molecular geometry can be tricky for students to grasp. Two-dimensional representations of molecular geometries predicted by the valence-shell electron-pair repulsion (VSEPR) model can be difficult to comprehend. Three-dimensional models, however, give students the opportunity to view and manipulate models as needed, making molecular geometry much easier to understand.

In this activity, each balloon represents an electron domain (either a bonding pair or a lone pair of electrons) surrounding a central atom. When connected, balloons naturally adopt the lowest energy arrangement predicted by the VSEPR model.

You can perform this activity as a demonstration, or alternatively, as a student investigation.

Students may incorrectly believe that the balloons in this activity represent electron clouds around the nucleus of an atom (rather than electron domains around a centrally bonded atom). Address the electron domain misconception as needed. Consider incorporating subsequent activities that use plastic molecular models. These products have colored atoms and use connectors to represent electron domains. Each atom connects to others using the appropriate molecular geometry.

AP students also struggle with predicting correct molecular shapes and bond angles. Consider assigning this activity as pre-course work over the summer or incorporating it in the end of course review.