Molecular Geometry Lab

Objective: Students will be able to figure out the shape of molecules using the VSEPR model. Materials: Play-Doh 6 Toothpicks (at least 4 different colors) Ruler Scissors Protractor Tape Piece of Colored Paper Piece of Scratch Paper Procedure: Part A: Making a Model

Methane (CH4) 1. Draw the Lewis structure for Methane. 2. Determine the electron arrangement, the molecular geometry, and the bond angle. Electron Arrangement: Look at the electron pairs around the central atom. 4 pairs = Tetrahedral 3 pairs = Trigonal Planar 2 pairs = Linear *double or triple bonds only count as one thing around the central atom. Molecular Geometry: Determine how many lone pairs you have around the central atom and then use the molecular geometry table. Bond Angle: Determine the bond angle by using the molecular geometry table.

3. Make a model of your molecule using the Play-Doh and the toothpicks. If a molecule has any lone pairs of electrons, show that by putting in a toothpick that is not bonded to anything. If a molecule has a double or triple bond make sure to use the appropriate number of toothpicks.

4. Tape the arrows onto each toothpick showing which atom is more electronegative. The arrows should point towards the more electronegative atom. Use your electronegativity chart to determine which atom it should point towards. 5. Determine if each molecule is polar or nonpolar and record it on the data table. Remember: Not Symmetrical = Polar Symmetrical = Nonpolar 6. Diagram your model including the arrows.

Notebook Data:

Methane CH4 Lewis Structure: Electron Arrangement: Molecular Geometry: Bond Angle: Polar or Nonpolar Diagram of Model:

Ammonia NH3 Lewis Structure: Electron Arrangement: Molecular Geometry: Bond Angle: Polar or Nonpolar Diagram of Model:

Water H2O Lewis Structure: Electron Arrangement: Molecular Geometry: Bond Angle: Polar or Nonpolar Diagram of Model:

Carbon Dioxide CO2 Lewis Structure: Electron Arrangement: Molecular Geometry: Bond Angle: Polar or Nonpolar Diagram of Model: Hydrochloric Acid HCL Lewis Structure: Electron Arrangement: Molecular Geometry: Bond Angle: Polar or Nonpolar Diagram of Model:

Oxygen O2 Lewis Structure: Electron Arrangement: Molecular Geometry: Bond Angle: Polar or Nonpolar Diagram of Model: Analysis Questions: 1. Why do molecules have a specific shape? 2. Compare your models of methane, ammonia, and water. Should the bond angles in these models be equal? Why or why not? 3. How can you tell if a molecule is polar or nonpolar? Can a molecule with polar bonds be nonpolar? Explain.