kinetic molecular theory written on a chalkboard in a chemistry lab

Everything You Need to Know About How to Teach the Kinetic Molecular Theory (States of Matter)

Reading Time: 4 minutes

Most people title this unit “states of matter,” and that’s fine. I like referring to this unit as the kinetic molecular theory unit to remind my students that matter is always moving! Also, this differentiates this unit a bit from what they learned in elementary or middle school. 

Much of this information will not be new to your students, so use this as an opportunity to enrich their current understanding! Students should know what a solid, liquid, and gas are… but can they represent them with particle diagrams? Can they fully describe the motion of those particles? If you change the temperature, what happens to the particles? 

We discuss the movement of particles in different states and how we can represent those differences on a phase diagram. It’s important to note that we are not discussing chemical reactions here. This unit focuses on the physical changes that matter undergoes. 

KMT Lesson Plans

Total Duration: 5.5 – 6.5 days

Note: a day refers to 45-50 minute periods.

Topic & TimelineTasksDescription
OPTIONAL Inquiry
1 day		Alt: Guided InquiryIf you have time/need an easy student-led activity to introduce this unit, this station activity from Kendo’s Chemistry store is great. I’ve done it before during SAT testing week. It’s completely self-paced and gets students thinking about states of matter at the particle level. 
States of Matter
1 day		Marble Demo


States of Matter Summary Chart		You’ll need some marbles and a sheet pan with higher edges for this demo. Place the marbles in the sheet pan and discuss the arrangement of the marbles when you “vibrate” the pan by moving it slowly. How do the particles move when you increase the energy input? 

If you have time, try showing a set of Eureka videos 
solids 
liquids

After this, we complete a States of Matter Chart as a class. 
Gases + KMT
1 day		Diffusion of a Gas Demo

Whiteboard and/or Class Brainstorming

Kinetic Molecular Theory Notes
 		Put something smelly on your desk. This can be a strong-smelling perfume a chemical (naphthalene is a common choice). Before you open the container, ask your students to raise their hands when they smell it and pay attention to the path. Be sensitive here to allergies.

Once everyone, or almost everyone, has smelled the chemical, ask your students to come up with the mechanism- how did the particles get from the container on my desk to your nose? You can do this as a class brainstorming session or in small groups.

Once your class has listed most, if not all, tenants of the KMT, have them take notes. They can copy your brainstorming notes from the board or complete more formal KMT notes.  
Temperature
1 day		Demo: Expansion of a Liquid
Whiteboard Discussion

Optional Additions
-Eureka: Measuring Temperature

–Reading: How does a thermometer work? 		Let’s take a bit more of a deep dive into temperature! Your students know that increasing temperature can cause a phase change, but what if we don’t add enough energy to change the phase? Use a thermometer as an example. 

For the demo, you’ll need two large test tubes. Fill one halfway with water and the other halfway with ethanol. Use food coloring to differentiate.  Close each test tube with a rubber stopper/glass tube apparatus. Place them both in a water bath. Heat the water bath on a hot plate. Ask your students to predict what will happen over time. Discuss what’s happening throughout the demo- ask for interpretations of their observations. You can stop the demo whenever you want, but definitely before the alcohol exits the top of the glass tube. 

In groups, have students draw particle diagrams of what they saw- water vs. alcohol. Why did the liquid rise? What’s going on here? What steps needed to occur for the water and alcohol to rise? Particles are constantly moving, but the hot water particles collide more often with the test tube than the particles inside the test tube. More energy is transferred into the test tube than out of the test tube because of these more frequent collisions. The liquid particles inside the test tube speed up and spread out to account for the increase in energy. An increase in the temperature reading represents this. 

Once your students understand how the hot water transferred energy to the test tubes, task them to draw particle diagrams for what would happen if you put the test tubes in an ice bath. 
Students should draw opposite diagrams. The faster liquid particles will collide more with the test tube than the water particles on the outside. More energy is transferred outside the tubes than in. Our less energetic liquid particles slow down and condense, resulting in a lower temperature reading.  
 
Changes to State
1 day		Phase Diagram Notes + PracticeDiscuss how helium and nitrogen are gases at room temperature. How do we fill a helium tank or get liquid nitrogen? Compression! But how can we compress a gas → temperature and pressure change!

Another set of Eureka videos would be great here: 
evaporation and condensation 
expansion and contraction.

We follow up our discussion with Phase Diagram notes. 
Review
1 day		Phase Diagram Practice

States of Matter Vocabulary Practice		Laminate a class set of phase diagrams. Give each student one, along with a dry-erase maker. Run through different scenarios of a sample of matter. Make changes to that sample and have your students predict which state the sample is in and if it completes a phase change to get there.
Assessment
0.5 days		I suggest a quiz or alternative assessment for this unit. It’s short and sweet; the assessment should be too!

Further Reading

The Chemistry Particle’s Guide to Teaching High School Chemistry, The Chemistry Particle

Classroom Resources: States of Matter, American Association of Chemistry Teachers

Frying Ice, ChemEdExchange

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  1. Pingback: The Chemistry Particle’s Guide to Teaching High School Chemistry - The Chemistry Particle

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