Mental models are created through your senses. What your body has touched and used helps your brain store it as a mental model. The more symbolic the concept, the more important it is to develop mental models for your students through hands-on activities.
Here’s a three-part sequence of what we do in our classroom to help students understand atoms and molecular motion in solids liquids and gases.
1. Cups & Pellets
Using three plastic cups and a handful of plastic pellets or BBs, try this with your students:
Completely fill the bottom of the first cup with a single layer of pellets.
In the second cup put enough pellets to cover about 1/3 the bottom in a single layer.
Place five pellets in the third cup.
Each cup represents a state of matter: solid, liquid or gas. Can you guess which is which? Gently shake each cup and note what you observe.
In the first cup, the solid, you should see that the pellets vibrate but don’t change position.
Rather than shaking the second cup, gently rock it back-and-forth. The pellets need to remain as a clump. You should notice that the positions of the pellets changes as well as the overall shape of the mass of pellets, however their volume does not.
Lastly, gently shake the third cup to see the pellets bounce and ricochet off the sides and each other. This is demonstrating the gaseous state.
2. Molecular Charades
Whenever possible, I love to get students up and moving to make their learning a full-body experience. This strategy is especially helpful for kinesthetic learners, but frankly, I think all benefit from it.
In this activity, each student will be a molecule of water. They’ll represent ice (the solid state), by linking arms. Here they can still move (vibrate), but they can’t change position.
Next, acting as liquid, they need to be always touching another person’s hands but they can constantly change which person they’re touching (think do-si-do in square dancing where they’re constantly grasping the next person‘s hand).
Next, they’ll pretend to be a gas (water vapor). Here they have no bonds—they should not be touching anyone, and they must move in a straight line at a constant speed. It’s important to understand that molecules don’t think and they should not change course or to try to hit or avoid hitting something or someone. When they bump into something—a desk, a chair, another student molecule—they can change direction.
Anytime we do an activity like this we always have a quick discussion ahead of time about how scientists act and why we’re doing this, and they know that if they can’t follow the principles, they become observers instead of participants.
Once they know how to show each state we play charades by dividing into groups and challenging each other to guess what state (or change of state) we’re demonstrating. These are the charade cards we use.
3. Molecular Stirrers
Set up some clear plastic cups with cool, warm, and hot water. Add a single drop of food coloring to each. Watch for the next few minutes and note what happens. Share observations and try to correlate what they’re seeing here with the two prior activities they’ve done. They should start to be able to visualize what’s happening at a molecular scale. The moving, vibrating, bouncing molecules are acting like little stirrers and mixing up the solutions. You can go beyond this by try to dissolve hard candy in water (this can take days)
Most of us need multiple exposures to the same concept before it begins to take root; it’s never once and done. We can’t teach a single lesson or activity and expect students to grasp it the first time they see it. This is why I like to have many activities focused on the same subject. Layering experiences like this helps kids to begin to develop a significant understanding of the concept and how it relates to other things they’re learning they begin to build a deep web of understanding much like the one that you and I have as teachers.