Lesson 8:
Molecular Models
Concepts conveyed | Materials | Procedure | Benefits
Concepts conveyed:
The purpose of this activity is to teach students in a hands-on fashion the molecular structure of some common molecules.
Materials:
One molecular geometry kit for every two to four students (each
contains, at least, one large Styrofoam ball, 5 smaller
Styrofoam balls, five toothpicks, and one small protractor in a
zip-closing storage bag).
Procedure:
Preface this activity with a lecture on molecular geometry. Then, ask students to form groups of two to four people each. Give each group a molecular model kit, and a name and chemical formula of a common molecule. Ask the students to form its geometry out of the Styrofoam balls and toothpicks that can be found in their molecular model kits. Walk around the classroom answering questions and make sure students are doing the exercise correctly.
For example: Ask students to form a methane molecule (CH4). This can be done by using one big Styrofoam ball for the center carbon and four smaller balls for the surrounding hydrogen atoms. Then, the four hydrogen atoms can be placed 109.5 degrees (using their protractors) from each another to form the tetrahedral geometry. Alternatively, the students could be asked to place the hydrogen atoms as far away from each other as possible around the central carbon atom, then students can use the protractor to measure the angle that results (109.5 degrees).
Examples:
Linear- BeF2, CO2, Cl2
Trigonal (triangular) planar- BF3, BCl3, GaF3, CH2O
Trigonal pyramidal- NH3, AsF3, H3O+
Angular or bent- H2O, NO2–, SnF2
Tetrahedral- CH4, CCl4, PO43-
Trigonal bipyramidal- PF5
Benefits:
- Students will be better prepared for laboratory experiments on molecular geometry.
- Working in small groups promotes teamwork and camaraderie.
- Creating the molecular models helps students to think in class and instructors to assess immediately the students’ understanding of material.