Valence shell electron pair repulsion(VSEPR) theory

The title of the Project: Valence shell electron pair repulsion(VSEPR) theory

This virtual laboratory is intended for use in chemistry classes on the following topics:

  • 10th grade. Chapter III. “Valence shell electron pair repulsion(VSEPR) theory”.

Objectives:

  • Apply VSEPR theory to predict the molecular geometry of a molecule.
  • Utilize the Gillespie method to determine electron geometry and molecular shape.
  • Construct and compare virtual models with real-life structures of molecules.

Practical part

This simulation by PhET allows students to explore and understand the relationship between electron arrangements and molecular geometries.

  1. Launch the simulation. There are two screens to use: “Model” and “Real molecules”. Click on the “Model” screen.

The Model Screen

This screen allows you to build your own molecules!

  1. In the center, you’ll see a basic 3D model of a molecule with one central atom and two single-bonded atoms. Click and drag to rotate it.

3. Click on the bonding icons to connect single-, double- or triple-bonded atoms to a model. Observe how the molecule’s shape changes as you add atoms.

4. You can add a lone pair of electrons to a model in this simulation.

5.Use the red button to remove atoms and electrons one by one or the yellow button to remove them all at once.

6.Checking the “Electron geometry” and “Molecule geometry” boxes in the “Name” section  displays the predicted molecular and electron shape (e.g., tetrahedral, linear).

7. You can show or hide the lone pairs of electrons by checking the “Show Lone pairs” box in the “Options” section.

8. Checking the “Show Bond Angles” box displays the angles between bonds. See how these angles change as you add atoms.

9. The “Reset” button clears the building area so you can start over.

The Real Molecules Screen

Let’s switch to the “Real molecules” screen through the navigation bar below. This screen showcases pre-built molecules for you to observe.

  1. Click the dropdown menu to choose a molecule from the list to investigate.

11. The central panel displays the chosen molecule’s real-life and model 3D structure

12. The “Name” and “Options” sections provide the same information as in the Model Screen.

Virtual experiment: The Gillespie method

Now let’s start experimenting.

  1. Select a molecule from the list to define its molecular geometry through the Gillespie method. For example, boron trifluoride (BF3).
  • Molecular formula is AX3Em. 
  • Through the formula given below, find the definition of m.

n – number of electron domains around the central atom. 

m – number of lone pair electron domains around the central atom. 

N₀ -total number of valence electrons on the central atom.

Nn – number of electrons donated by neighboring atoms (typically from forming a single bond), each single bond contributes one electron.

z – formal charge of the molecule

п- number of pi-bonds in a molecule.

  • Boron (B) has 3 valence electrons.
  • Each Fluorine (F) atom forms a single bond with Boron, contributing no lone pairs.
  • Total electron count around Boron = 3 (valence electrons) + 3 (bonding electrons from F) = 6
  • The number of lone pairs m=3-3=0 , molecule formula is AX3E0.
  • Since there are only bonding electrons and no lone pairs, the electron geometry for BF3 is trigonal planar (look at the Table 1 above).

Table 1.

  1. Now, switch to the “Model” screen and construct a 3D model of boron trifluoride (BF3).

15. In a “Real molecules” screen, select BF3 from the list and observe its real-life 3D structure. Compare this structure to your virtual model. Does it match your calculations? Try to define other molecules’ geometry.

Conclusion

This simulation provides a student-centered environment for exploring the fundamental concepts of bonding and molecular shapes. Through building virtual molecules and observing pre-built examples, students gain valuable experience in visualizing and predicting the three-dimensional structures of molecules. This interactive tool serves as a bridge between theoretical concepts and practical understanding, fostering a deeper appreciation for the world of molecular chemistry.