Intermolecular Forces Simulation — ClassAdapt
What the simulation shows
The simulation models how molecules behave at different temperatures by showing the intermolecular forces (IMF) between particles — the attractions that hold substances together. It uses water (H₂O) as the example molecule.
The coloured lines between particles represent bond strength: cyan = strong IMF, yellow = weakening, red = about to break. The bond meter at the bottom counts how many bonds are intact at any moment.
Solid — particles are locked in a regular lattice, vibrating in place. Nearly all bonds are cyan and intact. Temperature is far too low to overcome the attractions.
Melting — energy is added but temperature stays constant (latent heat). Bonds begin to stretch and snap — you see the cyan lines turn yellow then red. The lattice falls apart. This is what particle theory textbooks describe but rarely show happening.
Liquid — bonds continuously break and reform as particles slide past one another. No fixed shape, but particles still attract each other enough to stay close. The bond count drops but never reaches zero.
Boiling — another latent heat stage. Most remaining bonds are broken. Particles near the “surface” escape.
Gas — IMF are negligible. Particles move freely in all directions, bouncing off the container walls. Bond count is near zero. Note: the simulation runs without gravity, which is why particles don’t pool at the bottom in the liquid state — worth flagging with students.
Suggested class activity
“Bond detective” — predict then observe
Works well as a 15-minute paired activity, suitable for GCSE groups including lower-attaining pupils.
Setup: Display the simulation on the board (or share the link for individual devices). Start it paused on the Solid tab.
Task:
- Students write a prediction: “What do you think will happen to the bonds when we heat it to liquid?” — one sentence only.
- Run through Solid → Melting → Liquid in real time, pausing at each stage. Students annotate a simple three-column table:
| Phase | What I see happening to the bonds | What this means for the substance |
|---|---|---|
| Solid | ||
| Liquid | ||
| Gas |
- At the Liquid stage, ask: “The particles are still touching — so why can you pour water?” (Answer: bonds break and reform constantly, allowing particles to slide past each other.)
- At the Gas stage, ask: “Why is the bond count nearly zero but not zero?” (Opens discussion of condensation — particles occasionally get close enough for IMF to act.)
SEND adaptations: Use the Extra Slow toggle for processing time. Labels mode shows molecule identifiers. The bond meter gives a concrete number for pupils who find the visual hard to interpret. Irlen overlays available via the ♿ button.
Exit question: “A substance has very strong IMF. Predict whether its melting point will be high or low. Explain using the simulation.”