Atomic Interactions – Interactive PhET Simulation

Explore atomic interactions

As two atoms approach one another, they experience a combination of attractive and repulsive forces. The balance between these forces determines whether a stable separation between the atoms can be established.

This interactive PhET simulation allows you to investigate how the force and potential energy change with the distance between two atoms, and to see how attractive and repulsive interactions produce an equilibrium separation.

Move the atoms towards and away from one another and make predictions before checking the graphs. Look particularly for the distance at which attraction and repulsion balance, and connect this with the minimum in potential energy.

Atomic Interactions is provided by PhET Interactive Simulations, University of Colorado Boulder, and is used under the CC BY-NC 4.0 licence.

Try these challenges

1. Start with the atoms far apart
Place the two atoms a long distance apart. What do you notice about the force between them and their potential energy?

2. Bring the atoms closer together
Slowly decrease the distance between the atoms. At first, which interaction dominates — attraction or repulsion? What happens to the potential energy?

3. Find the equilibrium separation
Find the distance at which there is no resultant force between the atoms. What is significant about the potential-energy graph at this distance?

4. Move the atoms too close together
Push the atoms closer than their equilibrium separation. What happens to the force? Why does the repulsive interaction become so important at short distances?

5. Connect force and potential energy
Compare the force and potential-energy graphs. At what point is the potential energy at a minimum? What is the resultant force at this position?

6. Supply energy
Imagine trying to separate two atoms that are at their equilibrium separation. Why must energy be supplied to move them far apart?

7. Change the atoms
Try different combinations of atoms. Compare the depth and position of the potential-energy minimum. What does this suggest about the strength of the interaction and the equilibrium separation?

The key question

Keep asking:

How does the balance between attractive and repulsive forces change as the distance between two atoms changes?

A stable separation occurs when the attractive and repulsive forces balance and the system has minimum potential energy.

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