Molecule Shapes Simulation: Electron and Molecular Geometry with VSEPR

The Molecule Shapes simulation from PhET lets you build molecules in 3D by adding single, double and triple bonds and lone pairs to a central atom. You can see how electron groups push each other apart, tell electron geometry from molecular geometry, and compare your model with real molecules. It is free, runs in any browser on a phone, tablet or laptop, and it is a great fit for the chemical bonding and VSEPR lessons in Tamil Nadu State Board (Samacheer Kalvi) Chemistry.

What is the Molecule Shapes simulation?

This interactive simulation lets you build a molecule around a central atom and see its 3D shape. You can add bonds and lone pairs, turn the model around, and compare the angles in your model with the angles in real molecules. Because it runs on HTML5, there is nothing to install, and it works on phones, tablets, Chromebooks and computers.

PhET’s learning goals are to recognize that molecular geometry comes from repulsion between electron groups, to tell electron geometry from molecular geometry, to name both geometries for molecules with up to six electron groups, to compare the angles predicted by the model with real molecules, and to describe how lone pairs change bond angles.

Launch the Molecule Shapes simulation online

Tap or click inside the player and start exploring. Use the full-screen button in the player for a bigger view.

Credit: University of Colorado Boulder

How to use the Molecule Shapes simulation, step by step

1. Predict first. Before you build, say how many electron groups you will use and what shape you expect.
2. Add bonds. Add single, double and triple bonds to the central atom and watch the groups spread out.
3. Add lone pairs. Swap a bond for a lone pair and see how the shape and the angles change.
4. Name the geometries. Write down the electron geometry (all groups) and the molecular geometry (atoms only).
5. Compare with real molecules. Check your model against a real molecule, if that part is available in your version, and note how the real angles differ.

Tip for students: count the electron groups first. A double or triple bond still counts as one group.

The idea behind the simulation: electron geometry and molecular geometry

Electron groups = bonded atoms + lone pairs

Every bond (single, double or triple) and every lone pair around the central atom is one electron group. The electron geometry is the arrangement of all the groups: 2 groups are linear, 3 are trigonal planar, 4 are tetrahedral, 5 are trigonal bipyramidal and 6 are octahedral. The molecular geometry is the arrangement of the atoms only, so it changes when some of the groups are lone pairs. Lone pairs push harder than bonds, so real bond angles are often a little smaller than the ideal ones.

Worked example: Water has 2 bonded atoms and 2 lone pairs, so 4 electron groups. The electron geometry is tetrahedral, but the molecular geometry is bent. The ideal angle is 109.5°, but the real angle is about 104.5°, because the two lone pairs squeeze the bonds together.

VSEPR key terms explained

These are the words you will meet while using the Molecule Shapes simulation, with simple meanings.

Common mistakes: Counting a double bond as two groups, mixing up electron geometry with molecular geometry, and forgetting that lone pairs reduce the bond angle.

Try the VSEPR geometry finder (practice what you explore)

Choose the number of bonded atoms and lone pairs on the central atom. The finder gives the electron geometry, the molecular geometry, the ideal angle and a real example. Then tap a “what if” button.

What happens when you change a variable

Classroom activities for teachers

The Molecule Shapes simulation fits a single 40-minute period.

• Predict and test (10 min): students predict the geometry for a given set of bonds and lone pairs, then build it.
• Two geometries (10 min): students fill in a table of electron geometry and molecular geometry for 2 to 6 groups.
• Lone pair effect (10 min): students compare ideal and real angles for methane, ammonia and water.
• Exit ticket (10 min): students explain in two sentences why water is bent even though its electron geometry is tetrahedral.

Looking for the matching chapters? Browse the Chemistry books on TN SchoolBooks and download the Samacheer Kalvi PDFs, then use this simulation to make the chemical bonding lessons visual. More free science simulations and textbook PDFs are on the home page.

Quick quiz: test your understanding of VSEPR

Score: 0 / 5

Molecule Shapes simulation: frequently asked questions

The Molecule Shapes simulation turns invisible 3D shapes into something you can build, turn and compare with real molecules. Explore it, take the quiz above, and keep building until naming both geometries feels easy.