Grade Levels: 6-8, 9-12

In this lesson plan, adaptable for grades 6-12, students use an interactive simulation called Molecules and Light to examine how different wavelengths of light affect certain molecules.

Students will:

  1. Understand that light is made of photons that contain energy.
  2. Identify that energy increases from microwave to ultraviolet.
  3. Explore how light affects different molecules in various ways.
  4. Apply their knowledge to understanding the greenhouse effect on a molecular level.


  • Computers or other devices with internet access
  • Whiteboard
  • Paper


This lesson plan features an interactive simulation titled Molecules and Light, developed by our award-winning partner PhET through the University of Colorado Boulder. The simulation invites students to explore how light interacts with molecules in the atmosphere, discover the properties of greenhouse gases, and recognize the importance of the ozone layer.

Review the Molecules and Light Simulation Overview to learn about the sim controls, model simplifications, and insights into student thinking.

Preview and play with the Molecules and Light sim to plan how you will adapt it to your students’ needs.

Students should have a basic understanding of atoms and molecules, light as photons, and energy. This sim may seem advanced, but the concepts behind it are intuitive and easy to understand.

This lesson may be conducted using partners.

Build background knowledge or reinforce topics with these BrainPOP movies: Compounds & Mixtures, Chemical Equations, Chemical Bonds, Atomic Model, Periodic Table of Elements, Greenhouse Effect, and Electromagnetic Spectrum.

Lesson Procedure:

  1. Play the BrainPOP movie Greenhouse Effect on a whiteboard or other display. Explain that this lesson will focus on how greenhouse gases work on a molecular level.
  2. Instruct students to open the Molecules and Light sim and familiarize themselves with the controls and features. Have your students experiment with some of the molecules and light interactions and record their observations in their notebooks.
  3. Have students to share their findings in a few descriptive words. List their responses on the whiteboard. Older students may want to create a table to document their findings more thoroughly: Molecules_and_Light_Lesson_Plan_-_Google_Docs
  4. Reflect on how molecule behavior changes in general from microwaves to UV emission. Use the “Show Light Spectrum” to confirm your reflections. Older students may use appropriate knowledge such as Lewis dot diagrams to explain these behaviors.
  5. Ask students which molecules were not affected by any of the radiation and why. Give a few minutes for them to think and talk to a partner to come up with reasons why.
  6. Have students specifically look at how infrared light interacts with these molecules again. Using the SnapThought tool, instruct students to take some snapshots of these instances and write a few sentences describing why this interaction would lead to a greenhouse effect. Older students may use their knowledge of vibration and friction to discuss this from a physics perspective.

Extension Activities:

Water vapor is a big component of greenhouse gases because it creates a positive feedback loop: the warmer the climate, the more likely that water vapor will exist in the atmosphere, which will warm the planet even more. However, CO2 and CH4 are our biggest concern. Have your students research why water vapor is not as concerning as these other greenhouse gases. (Hint: the answer has to do with how clouds act as reflective surfaces and how long these gases live in the atmosphere.)

Advanced students (requires knowledge of wavelengths): UV light breaks O2 into free oxygen atoms that combine with other O2 molecules to form O3. UV light then breaks O3 into O2 and O, as shown in the simulation. This is called the ozone-oxygen cycle. Why doesn’t the UV light break O2 down in this simulation?

Filed as:  6-8, 9-12, Molecules and Light