The molecular motion demonstrator can be used to dramatically illustrate the intermolecular structure of substances in various states, such as solid, liquid and gas. It can also demonstrate molecular random motion, molecular distances, kinetic theory and concepts related to the results of altering the molecular structure of specific substances.
- Molecular motion
- liquids and gases
- Kinetic molecular theory
The material things around us are all various types of matter. Matter is anything that takes up space and has mass. Matter can exist in three different physical states: solid, liquid and gas. A solid is matter that has a definite shape and volume. A solid does not depend on the shape or volume of a container. A liquid is a form of matter that flows, has a fixed volume and takes the shape of its container. A gas is matter that takes the shape and volume of its container.
The word kinetic means motion. The kinetic theory states that the tiny particles in all forms of matter are in constant motion. These particles may be atoms, ions or molecules of gases, liquids, or solids. In the Molecular Motion Demonstrator the various states of matter will be visualized using small metallic spheres (BBs) to represent the particles in matter. The BBs can be placed in motion by gently or vigorously shaking the motion demonstrator from side to side. The arrangement and activity of the BBs in the apparatus can be used to represent the different states of matter as well as to observe the changes that occur on the atomic or molecular level during changes of state (e.g., melting, boiling, freezing).
Copper shot (BBs)*
Molecular Motion Demonstrator*
*Materials included in kit.
This activity is considered safe. Follow all normal laboratory safety rules.
The BBs can be removed from the tray and stored. The apparatus can be reused many times.
Practice using the device on an overhead projector before demonstrating with it to the class. With a little practice you will become adept at shaking the apparatus to illustrate key ideas while keeping the BBs in focus on the overhead. Use the demonstrator with various lessons during different times of the year to illustrate the nature of matter and molecular motion.
- To represent the three states of matter, fill the demonstration tray as follows:
Gas: ⅓ full
Liquid: ⅔ full
Solid: nearly full
- Gently shake the tray slightly above the glass on an overhead projector. Find the focal plane so that the BBs are clearly visible on the screen. Note: The particles in the solid state should be closely packed so that only rotational and vibrational motions of the particle are possible.
- Have students describe the nature of each state of matter as represented by the BBs. Have them describe how the different states of matter are alike and how they are different.
- Heating and Cooling Solids
In the preparation of metals, metallurgists often change the nature of metals by heating and cooling the metals in different ways. Different treatments result in different final arrangements and give metals different final properties. Annealing, hardening and tempering of metals are examples of different treatments. These processes can be illustrated with the BB arrangements in the demonstration tray.
- Annealing results when iron is heated red hot and then slowly cooled. Annealing results in the iron atoms arranging themselves into more perfect crystals. This process makes the metal easier to bend. To visualize the annealing process, fill the tray about ⅔ full with BBs and slowly rotate the tray in a circular fashion to simulate the slow, red-hot heating process followed by slow cooling. Slowly tilt the tray to about a 10° angle and continue to use short little shakes to get the BBs to line up in a nice crystalline lattice. The BBs should be perfectly lined up all in rows and columns. This arrangement of iron atoms makes it easy to bend.
- Hardening results when metal is heated and then allowed to cool quickly. When cooled quickly, the atoms do not have a chance to line up in a neat crystalline pattern as they do when they are annealed. Instead, they line up in a disorganized pattern resulting in a metal that is hard and brittle. Knife blades and drills are made of hardened metal. Simulate this process by slowly rotating the tray again until the BBs are all spread out. Then quickly stop the movement while tipping the tray quickly at a 10° angle. The BBs should form a disorganized array in the tray and should be very different than the annealed structure.
- Tempering of metal is accomplished by hardening the metal (b) followed by gentle warming and slow cooling of the metal. This process results in a metal that has properties intermediate between those annealed (easily bent) and those hardened (nearly unbendable). Tempered metal is often used to make things like springs. The demonstration to illustrate the tempering process starts with a repeat of b (hardening). After showing a hardened pattern of BBs, gently shake the tray until slightly more than half the BBs line up (to show slow warming) and then stop (to show cooling). The result will be a pattern that resembles a mixture of a and b.
- Without physical damage, the molecular motion demonstrator can be reused many times.
- It is imperative to practice the techniques in this demonstration to achieve the desired visual effects.
- With your imagination, the tray and BBs can be used to illustrate other principles of molecular motion.
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering Practices
Developing and using models
Disciplinary Core Ideas
MS-PS1.A: Structure and Properties of Matter
MS-PS3.A: Definitions of Energy
HS-PS1.A: Structure and Properties of Matter
HS-PS3.A: Definitions of Energy
Systems and system models
Structure and function
Stability and change
MS-PS1-2: Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.