Explore molecular shapes in 3D Molecular shape is determined by the arrangement of electron pairs around a central atom.
This interactive PhET simulation allows you to explore how bonding pairs and lone pairs repel one another and how these repulsions determine the shapes and bond angles of molecules.
Don't just look at the shapes — experiment with the model.
Add and remove bonding pairs and lone pairs, predict the shape before you reveal it, and rotate the molecule to examine its three-dimensional structure.
Molecule Shapes is provided by PhET Interactive Simulations, University of Colorado Boulder, and is used under the CC BY-NC 4.0 licence.
Use the simulation to investigate each challenge.
Make your prediction before revealing the molecular geometry or bond angles.
1. Start with bonding pairs only
Place two bonding pairs around the central atom.
Predict their arrangement before displaying the geometry.
Now repeat with three, four, five and six bonding pairs.
Can you explain why each arrangement keeps the electron pairs as far apart as possible?
2. Investigate tetrahedral geometry
Create a central atom surrounded by four bonding pairs.
Display the bond angles.
What shape do you obtain, and what is the ideal bond angle?
3. Replace a bonding pair with a lone pair
Starting with four bonding pairs, remove one bonding pair and replace it with a lone pair.
You now have three bonding pairs and one lone pair.
Predict what happens to the shape and bond angle.
Why does the bond angle become smaller?
4. Add a second lone pair
Now arrange two bonding pairs and two lone pairs around the central atom.
Predict the molecular shape.
Compare its bond angle with the previous arrangement.
Can you explain the further reduction in bond angle?
5. Compare CH₄, NH₃ and H₂O
Use the Real Molecules section to investigate methane, ammonia and water.
All three can be considered as having four electron pairs around the central atom.
Why are their molecular shapes and bond angles different?
6. Investigate five electron pairs
Create a trigonal bipyramidal arrangement.
Now replace bonding pairs with lone pairs.
Does it matter where a lone pair is placed?
Use the model to investigate why lone pairs prefer equatorial rather than axial positions.
7. Investigate six electron pairs
Start with six bonding pairs to produce an octahedral arrangement.
Replace one bonding pair with a lone pair and then another.
Predict the resulting molecular geometries before revealing them.
The key question
As you work through the simulation, keep returning to one idea:
How does electron-pair repulsion determine the three-dimensional shape of a molecule?
Don't try simply to memorise a list of shapes. If you understand the repulsions between electron pairs, you can work out the shape.