Introduction to Molecular Dynamics Models

Interactive, scaffolded model

Important Notice!

The system can gain too much energy if there are many highly charged atoms. If this happens, cool the system with the blue arrow below the thermometer.

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Overview and Learning Objectives

The three pages of the activity follow a sequence of introducing the basic controls, the properties of the main model elements, and their primary interactions. The user is encouraged to learn to use the icons to interact with the model and to plan experiments.

Students will be able to understand the basic operation of the Molecular Workbench and identify what forces are important at the atomic scale.

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Classroom Practice

To avoid jargon, the van der Waals force is called simply "atom-atom attraction." Once students are familiar with the concept, introduce the term because it will be used extensively in other activities.

You might also point out that atoms with plus and minus charges attract. This is in addition to the van der Waals forces.

Ask that students provide evidence for any claims they make.

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Central Concepts

Key Concept:

Atoms interact with each other and with external fields. The strongest forces are electrostatic; gravity is negligible.

Additional Related Concepts

Physics/Chemistry

• Atom
• Charge
• Collision
• Container
• Gravitation
• Kinetic energy

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Extensions and Connections

The movement of charged objects in an electric field is used extensively in science and technology. This is, for instance, how electrophoresis works. Students can experiment with various fields and charges.

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Additional Info

Additional Background

Gravity has no effect at this scale. It would take three years for an atom to fall the width of the container!!!

The atom-atom attraction is actually due to electrostatic forces. A fluctuation in one atom creates an electrical dipole that induces an attractive dipole in any nearby atoms. This only works at close distances.

Additional Questions

How do the atom-atom forces change the spatial arrangement of the atoms?

[When the force is on, the atoms clump. This shows how the liquid and solid states rely on atom-atom forces.]

How does the representation of atoms differ from reality?

[Real atoms lack color, velocity vectors, + and - signs, and sharp edges.]

What good is a model that does not accurately mirror reality?

[No model is perfect. Model making always involves simplification and the resulting models always have to be checked against reality.]

Give evidence for atom-atom repulsion.

[The atoms bounce off each other and do not interpenetrate due to a repulsive force.]

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Activity Credits

Created by CC: Molecular Literacy using Molecular Workbench

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Requirements

• Java 1.5+ - Java 1.5+ is available for Windows, Linux, and Mac OS X 10.4 and greater. If you are using Mac OS X 10.3, you can download MW Version 1.3 and explore within it instead.

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Technical Notes

The thermometer measures the average kinetic energy per particle. This is what temperature is. Pressing the red arrow increases the speed (and hence the kinetic energy) of every atom. The green arrow has the opposite effect.

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