Atomic interactions

The title of the Project: Atomic interactions

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

  • 10th grade. Chapter I. “Atomic structure”.


  • Explore the attractive and repulsive forces between atoms
  • Investigate the relationship between potential energy, distance between atoms, and atomic interactions

Practical part

Here’s a step-by-step guide on how to use the PhET simulation “Atomic Interactions”:

  1. Choose your atom pair:  The simulation allows you to explore interactions between different elements. Start by selecting an atom pair, like Argon-Argon, from the available list.

2. Observe the potential energy graph:  Below the graph, you’ll see two atoms. One is fixed, and you can move the other. The graph shows the potential energy (y-axis) versus the distance between the atoms (x-axis). The position of the movable atom is reflected on the graph.

3. Explore the distance and energy relationship: Observe the changes in potential energy on the graph. Move the unpinned atom closer:As the distance decreases (atoms get closer), the potential energy becomes more negative (deeper well on the graph). This indicates an attractive force, likely due to temporary fluctuations in electron distribution (van der Waals forces).

    4. Move the unpinned atom very close: The potential energy sharply increases (steep rise on the graph) as the atoms get too close. This represents a strong repulsive force that prevents atoms from completely overlapping. This aligns with the Pauli repulsion principle, where electrons in the same orbital repel each other. If the atom goes off-screen, use the “Return atom” button to bring it back.

    5.Visualize the forces:  Open the “Forces” panel. You can choose to display “Total Force” or separate “Attractive” and “Repulsive” force vectors. This can help you visualize the forces acting on the atoms as you move them.

    6. Control the simulation speed:  Use the simulation controls to pause, step forward, or slow down the movement of the unpinned atom. This allows you to observe the changes more closely.

    7. Compare bonded and non-bonded pairs:  Reset the simulation and choose a different atom pair, like Neon-Neon (non-bonded) or Oxygen-Oxygen (bonded). Compare the shapes of the potential energy graphs for these pairs.

    8. Analyze the graph:  Use the zoom tool to see the entire potential energy graph clearly. This might help you understand the significance of values below zero for potential energy (which can be a challenging concept for some).

    9. Identify sigma and epsilon:  Once you’ve compared bonded and non-bonded interactions, try to determine the meaning of sigma (σ) and epsilon (ε) based on the shapes of the corresponding graphs.Sigma (represented by the bump on the repulsive side) relates to the distance at which the repulsive force dominates. Epsilon (the depth of the attractive well) reflects the strength of the attractive force. These parameters define the Lennard-Jones potential, a mathematical model that captures both attractive and repulsive forces between atoms.

    10. Explore custom attraction:  This feature allows you to investigate how atom size and interaction strength affect the potential energy. Zoom back in on the graph if needed.

    11. Modify atom diameter:  Change the atom diameter using the slider or by dragging the arrow on the graph. Observe how both the graph and the atom representations update dynamically.

    12. Adjust interaction strength:  Use the slider or the graph arrow to modify the interaction strength. See how this dynamically affects the potential energy graph.

    13. Analyze relationships:  Relate the changes in atom diameter, interaction strength, and the resulting shape of the potential energy graph. This can help you understand how these factors influence the attraction between atoms.


      The PhET simulation provides an interactive tool to visualize the interplay between attractive and repulsive forces acting on atoms. By manipulating the simulation, students observed how changes in distance, bonding, atom diameter, and interaction strength affect the potential energy graph.