This reading describes how chemists modified the molecular structures of CFC to create HFCs and in doing so, created ozone-safe refrigerants. The underlying chemical concept of the reading is that molecular structure determines a compound's properties, and that changing the molecular structure will change the properties. The students should grasp the technological application of this concept to create new molecules with desired properties by creating new molecules with specifically designed molecular structures.

This reading is rich in other chemistry which you may choose to discuss at your own discretion, depending on the abilities and skill levels of your students. A few topics you may choose to include are discussed below:

Depending on the abilities of your students you may choose to discuss the reasons why HFCs are thought to be safer for the ozone layer than CFCs. The students will have read in earlier sections how the chlorine atoms in the CFC molecules are responsible for the reaction cycle which depletes ozone.

HCFCs and tropospheric decomposition

Before HFCs, compounds called hydrochlorofluorocarbons (HCFCs) were introduced as CFC alternatives. Though still containing carbon-chlorine bonds, they also contained carbon-hydrogen bonds which, which are more susceptible to being broken under conditions in the lower atmosphere. This would, in theory, make them less likely to linger in the atmosphere long enough to reach the stratosphere and cause ozone damage.

Additional teacher resources, at other Web sites...

Refrigerants for the 21st Century — an in-depth case study on the search for alternative refrigerants, from ChemCases at Kennesaw State University. This module is designed to foster knowledge as well as critical thinking. It is designed for the college level, but some material can be adapted for high school or middle school use. It is also an excellent source of teacher background information.

Relevant National Science Education Standards

Unifying Concepts and Processes — The reading deals with our attempts to create refrigerants which do not interfere with the chemical systems operating in the earth's atmosphere. Likewise, it deals with the system of refrigerant molecules themselves, and how their interacting parts (atoms and chemical bonds) contribute to the overall behavior of the molecules.

Physical Science — The reading deals with the molecular nature of matter, chemical reactions, and the interaction of matter with energy in the form of UV radiation.

Earth and Space Science — The reading deals with the quest to create refrigerants which do not interfere with the geochemical cycles which keep ozone safely over our heads.

Science and Technology — The reading probes one angle, testing, of the technology of designing ozone-safe refrigerants.

Science in Personal and Social Perspectives — The reading involves an environmental quality issue which is also a human-induced health hazard, plus the use of science in overcoming this global challenge.

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