Summary

In this lesson, students will learn about the history of chlorofluorocarbons (CFCs) and the harm they cause the ozone layer through an article reading. There are a series of activities to help promote literacy in the science classroom related to the reading. This lesson could be easily used as plans for a substitute teacher, as most of the activities are self-guided.

Grade Level

High School

NGSS Alignment

This lesson will help prepare your students to meet the performance expectations in the following standards:

• HS-PS1-1: Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.
• HS-PS1-2: Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.
• Scientific and Engineering Practices:
  • Asking Questions and Defining Problems
  • Constructing Explanations and Designing Solutions
  • Engaging in Argument from Evidence
  • Obtaining, Evaluating, and Communicating Information

Objectives

By the end of this lesson, students should be able to:

• Understand that electromagnetic energy can break bonds and cause chemical reactions.
• Identify the parts of Earth’s atmosphere.
• Realize that there isn’t one chemical solution to all problems or processes.
• Associate a real-life example of when scientists disagree and must defend their interpretation of data.

Chemistry Topics

This lesson supports students’ understanding of:

• Free Radicals
• Energy
• Radiation
• Chemical Reactions
• Chemical Bonds
• Refrigerants
• Physical Properties
• Chemical Properties
• Molecular Structure

Time

Teacher Preparation: 10 minutes
Lesson: Approximate times for students to complete each activity in the lesson:

• Reading: 20 minutes
• History exercise: 15-20 minutes
• Perceptions of chemicals: 15-20 minutes
• CFC debate: 15-20 minutes
• Atmospheric reactions: 15-20 minutes

Materials

• Reading document and desired handouts to accompany the reading.

Safety

• No specific safety precautions need to be observed for this activity.

Teacher Notes

Background:

• This lesson plan was originally developed through the American Chemical Society’s National Historic Chemical Landmarks Program. Under this program, ACS grants Landmark status to seminal achievements in the history of the chemical sciences and provides a record of their contributions to chemistry and society in the United States.

• Before assigning the reading, preview/review vocabulary that students will encounter. Terms can be split among students to research online or in a chemistry textbook, then share with the entire class.
  • Refrigerant: In general, liquid compounds with low boiling points used in refrigerators and air conditioners that conduct/absorb heat well.
  • Chlorofluorocarbons (CFCs): Compounds that contain carbon, fluorine and, chlorine. Some CFCs are nontoxic and nonflammable refrigerants, developed in the 1930s to replace toxic and flammable options.
  • Ozone (O₃): A reactive molecule made up of three oxygen atoms. It can be found near Earth’s surface as a pollutant in photochemical smog. It is also found higher up in the atmosphere, where it absorbs potentially damaging ultraviolet (UV) radiation.
  • Troposphere: The part of the atmosphere from Earth’s surface up to about 6 miles.
  • Stratosphere: The part of the atmosphere from 6 to 31 miles above Earth’s surface.
  • Inert: A substance that is stable and does not tend to react.
  • Volatile: The tendency of a chemical to vaporize (to turn from liquid to gas).

Lesson Overview:

The lesson includes the multiple components, as outlined individually below. The Reading is essential for all of the activities. Teachers can choose to do one or all of the included activities. Student handouts and corresponding answer keys are provided for each item described below:

• Reading: Chlorofluorocarbons and Ozone Depletion
• Activity: History Exercise
  • Events related to CFCs, environmental effects, and legislation to limit CFC use took place over a number of years. Students identify what happened when, and then are asked to consider how the story played out now that they have an idea of the science and how decision makers collaborate.
• Activity: Perceptions of Chemicals
  • Students work their way through the changed perception of CFCs as more information was learned about the class of chemicals. They realize the perception of a chemical, whether positive or negative, isn’t always a clear-cut decision.
• Activity: CFC Debate
  • Debate issues already experienced and outline challenges CFCs presented the world. They then are asked to think ahead to a more recent CFC situation experienced in 2018.
• Activity: Atmospheric Reactions
  • The reactions between CFCs and UV light and their effects on ozone in the stratosphere are examined. Students compare this damaging affect to another reaction with ozone that is generally viewed as positive.

• Related classroom resources from the AACT library and ACS that may be used to further teach this topic:
  • Lesson: The Ozone Layer
  • AP Lesson: The Downside to Catalysts
  • C&EN Speaking About Chemistry video: “Keeping Cool Without Killing the Planet”
    • The video gives an overview of the use of refrigerants, from the toxic, flammable compounds used in the 1920s, to the nontoxic, nonflammable CFCs developed in the 1930s to replace them. The video points out that while new compounds solved some the old problems, they brought new problems, such as ozone depletion. It also extends this point to more recently developed refrigerants.
  • ACS Reactions video: “How Air Conditioning Works”
    • It provides an explanation of how refrigerants, including CFCs, work to keep things cool as part of refrigerators and air conditioners.
  • Students could also read the April 2013 ChemMatters article “In the Fog about Smog” by Ginger Butcher. Butcher wrote this when she was the Education & Public Outreach lead for NASA’s Aura Mission, which studies Earth’s ozone, air quality, and climate.
  • Accompanying ChemMatters video: “How NASA Keeps Tabs on Air Pollution from Space.”
    • The video discusses the Aura satellite and its instrumentation, along with different roles that ozone plays in varying locations in the atmosphere.
      
• Other useful links:
• National Historic Chemical Landmark: Chlorofluorocarbons and Ozone Depletion