Are you looking for fun ideas for teaching your states of matter unit in middle school science this year? Phase changes are one of the most misunderstood concepts in science. Check out how I teach MS-PS1-4 in my classroom!
How do you address misconceptions in a states of matter unit?
Start by exposing the gaps. Most students can name condensation, melting, and boiling, but they can't explain where the water on a cold can comes from. Build understanding with molecular models first, then layer in vocabulary, so students reason about what atoms are actually doing during a phase change.
Have you ever asked your students to explain why water forms on the outside of a cold soda can when they take it out of the fridge? They may be able to say that it is condensation. But, ask them to explain from where the water forming around the can originates. They might say it is water “leaking through the can”. If they know the definition of condensation, they may say it comes “from the air”.
Phase changes may be the most misunderstood science concept I teach. Students usually know (or have at least heard of) the definitions such as condensation, melting, boiling, and freezing. However, their ability to discuss these concepts falls apart after that.
I believe the answer to helping students have a full understanding of changes in states of matter is developed using models. Here is my sequence for teaching my MS-PS1-4 States of Matter Unit to my middle school science students.
- Understanding Molecular Models of Solids, Liquids, and Gases
- How Do Atoms Gain Energy?
- Exploring The Connection Between Phase and Heat
- Explaining Phase Change Graphs
How do molecular models show solids, liquids, and gases?
Solids, liquids, and gases look different at the atomic level because of how much energy their atoms have. In a solid the atoms are locked in place; add energy and they slip past each other as a liquid; add more and they fly apart as a gas. Represent atoms as simple circles and show energy with short or long arrows.
Students need to be able to understand that solids, liquids, and gases look different on an atomic level. The atoms in solids are close enough to each other that they cannot move or slip by each other. This allows solids to maintain their shape.
Atoms in a liquid have more energy than the same types of atoms in a solid. With more energy, they move more quickly much like students who eat too much candy! With more energy, the atoms can begin to slip by each other. This allows them to take the shape of their container.
If atoms gain even more energy, they will become a gas. These atoms have even more energy than liquids and push other atoms apart as they bounce off each other. This is why gases take up much more space than liquids – the atoms are pushing each other more than in a liquid.
For molecular models in this unit, I like to represent atoms as simply a circle. Students do not need to have an understanding of the parts of an atom for this standard. I like to represent energy in qualitative terms by showing the atom with shorter arrows (less energy) or longer arrows (more energy).
How do atoms gain energy?
As matter heats up, its atoms gain energy and move faster, bouncing off each other and spreading out. We measure that energy as temperature: higher temperature means more energy and more movement, and lower temperature means less. This is the key link students need to connect heat and phase change.
The next important piece of information students need to develop a full understanding of this standard (MS-PS1-4) is understanding how atoms gain energy. As atoms heat up, they gain more energy and move faster. This causes them to bounce off each other and spread out.
We measure the amount of energy atoms have by measuring their temperature. Higher temperature means more energy in the atoms and more movement. The opposite is true for lower temperatures.
How can a PhET simulation help teach phase changes?
The PhET States of Matter lab lets students raise and lower the temperature of different substances and watch the atoms respond. It is inquiry-friendly: give them five minutes to play, and they start estimating melting and boiling points and asking their own questions before you ever define a term.
If you’ve read my other articles about modeling, you’ll know that I love PhET digital labs. They are designed to be easy to use in classrooms. They are simple enough for students to discover important concepts through inquiry but also detailed enough to be used in elementary grades, middle school, and high school.
This PhET lab is no different. Students can raise or lower the temperature of different types of matter (atoms and molecules) and see what happens to the atoms. They can make observations about the effects of heat on atoms and gain a conceptual understanding of phase changes.
I like to challenge students to estimate the melting and boiling points of atoms using this model by observing how the atoms respond to heat. When the atoms begin to move apart from each other and spread around the container, it has become a liquid. When the atoms begin to fly around the container, it has become a gas.
These activities do such a great job of allowing students to discover science concepts – and students think they are fun! I usually give them five minutes to just play around with the simulation and make observations. They will usually discover the beginnings of a concept on their own and even develop their own questions!
How do you teach phase change graphs?
Heating and cooling graphs show students something surprising: as water boils, its temperature stays at 100°C until all the liquid becomes gas. The energy isn't disappearing—it's breaking bonds. Give students practice labeling the parts of the graph and finding melting and boiling points for different substances.
Another important conceptual understanding of states of matter is reading a graph and determining what kind of phase changes are occurring. Most students do not know that, as water begins boiling, its temperature remains at 100°C until all the liquid has changed into a gas. It’s also important for students to know that the energy is not disappearing – it is being used to break bonds between atoms and allow them to change phase.
Students need to have practice evaluating a heating or cooling graph and labeling the parts of the graph. It’s also a good idea to show them different graphs for different atoms or molecules. You should also ask them to determine the melting and boiling point of these atoms or molecules from the graph.
I have this full unit for sale in my TpT store – check it out!
What review games work for a states of matter unit?
Conceptual understanding comes first, but students still need vocabulary practice with solids, liquids, gases, and the phase-change processes. Bingo built from definitions and digital escape rooms both work well—they let students confirm what they know while keeping the review engaging.
Most of our efforts when teaching states of matter in middle school science should be towards conceptual understanding of these processes. However, practice with vocabulary is also important. Students need to be able to identify and use the definitions of solids, liquids, and gases as well as phase change processes (sublimation/deposition, melting/freezing, and boiling/condensation).
I use several different games to review these terms and concepts. One of my favorite ways to review is using bingo boards. I have students write 24 different terms on a bingo board. Then, I read a clue for one of those terms (not the name of the term). Students mark off the term on their board. I like to use bingo this way because each student know they can mark off a term on their board as long as they know the definition. I also have students work together sometimes to help each other in case one of them doesn’t know a term. Here is a link to three different review games for teaching states of matter in my TpT store.
Another fun way to review is using digital escape rooms. Students explore a room and find hidden clues about states of matter. When they answer a question, they get a letter to the password. After they gather all the letters, they unscramble the letters to find the password to escape!
Click here to check out my states of matter escape room in my TpT store – one of my best sellers!
States of matter is one of those concepts that students have been taught many times before. And, students usually believe they completely understand it. They often have a surface-level understanding of phase change processes and the definitions. Building conceptual understanding of states of matter through molecular models and graphs will help them throughout their middle school science classes. As they progress to the water cycle and chemistry, these models will deepen their understanding of more complicated subjects.