Unit Plan 7 (Grade 8 Science): Thermal Energy & Particle Motion

Focus: Explain how adding or removing thermal energy changes particle speed, temperature, and states of matter (solid, liquid, gas) using models and data. Connect everyday heating and cooling situations to particle motion and phase changes, emphasizing that particles are always moving and that energy changes their motion, spacing, and state.

Grade Level: 8

Subject Area: Science (Physical Science • Matter & Its Interactions • Modeling)

Total Unit Duration: 5 sessions (one week), 50–60 minutes per session

I. Introduction

Students build on their particle model of matter to explain what happens when substances are heated or cooled. They examine how thermal energy affects particle speed and spacing, leading to state changes like melting, freezing, evaporation, and condensation. Through simple labs, temperature–time graphs, and particle diagrams, students learn to predict and describe what will happen in different thermal scenarios (e.g., ice in a drink, warm air rising, condensation on a cold window). They practice connecting macroscopic observations (melting, boiling, fogging) to microscopic particle motion.

Essential Questions

• How does adding or removing thermal energy change particle motion and temperature in a substance?
• What happens to particle arrangement and spacing when substances change state (solid ↔ liquid ↔ gas)?
• How can models (particle diagrams, graphs) help us predict and describe what will happen during heating or cooling?
• Why are some temperature changes smooth while others show plateaus during phase changes?
• How does understanding thermal energy and particle motion help us make sense of everyday phenomena like boiling water, condensation on windows, or ice packs?

II. Objectives and Standards

Learning Objectives — Students will be able to:

1. Describe and compare particle motion and spacing in solids, liquids, and gases.
2. Explain that thermal energy is related to the motion of particles and that adding/removing energy changes particle speed and sometimes state.
3. Collect and interpret temperature–time data for a simple heating or cooling process and relate features of the graph to particle behavior.
4. Develop and revise particle models that show how particles move, how far apart they are, and what state they are in when thermal energy is added or removed.
5. Use models to predict what will happen to particle motion and state in new thermal scenarios (e.g., cooling steam, warming ice, using an ice pack).
6. Create a final model-based explanation (diagrams + written reasoning) that aligns with MS-PS1-4 by describing changes in particle motion, temperature, and state in a chosen situation.

Standards Alignment — 8th Grade (NGSS-based custom)

• MS-PS1-4 — Develop a model that predicts and describes changes in particle motion, temperature, and state when thermal energy is added or removed.
  • In this unit, students create and refine particle diagrams and temperature–time graphs to show how energy changes matter’s state and motion.

Success Criteria — Student Language

• I can describe how particles move and how close they are in solids, liquids, and gases.
• I can explain how adding thermal energy makes particles move faster (and often farther apart), while removing energy makes them move slower (and often closer together).
• I can read and interpret a temperature–time graph and connect it to what particles are doing during heating or cooling.
• I can draw particle models that show changes in motion and state when something melts, freezes, boils, or condenses.
• I can create a model that predicts what will happen to particles in a new heating or cooling scenario and explain my reasoning clearly.