Greenhouse Gases

Contextualize

The analysis of the composition and structural characteristics of greenhouse gases, their interactions with electromagnetic radiation in the atmosphere, and the effects of those interactions on average temperatures on our planet serve to introduce and apply central concepts in chemistry such as electronegativity, partial charge, bond polarity, molecular polarity, and light-matter interactions using a systems thinking perspective. This context is ideal for exploring or reinforcing the central idea that the composition and structure of chemical substances at the submicroscopic level determine their physical properties.

Focus

For example, this infographic explicitly indicates the systems and components in interaction analyzed during the proposed lesson on greenhouse gases in the atmosphere. The analyses and discussions focus on the properties of chemical substances in the atmosphere that absorb the infrared solar radiation reflected by Earth. The consequences of these interactions on our planet's temperature and life on Earth are also considered.

Define

Central Ideas

The physical properties of any substance are determined by its composition and structure at the molecular level.
Light-matter interactions in the atmosphere depend on the nature of the electromagnetic radiation and the composition and molecular structure of atmospheric components. These interactions induce physical changes that affect the environment.
The atomic composition and structure of a molecule affect the distribution of valence electrons in bonds and may lead to the uneven distribution of charge in the system. The presence of partial electric charges of opposite signs on bonded atoms makes the bond polar, and a nonsymmetrical distribution of charge in the molecule makes the molecule polar.
Greenhouse gases in the atmosphere absorb infrared radiation because they are comprised of molecules that undergo vibrations that alter their molecular polarity.
Absorption of infrared radiation alters the energy state of molecules. The energy absorbed is transferred to surrounding molecules via collisions, increasing the temperature of the system.
The global warming potential of a greenhouse gas depends on the composition, structure, and mass of its molecules, the different vibrational modes that these molecules can adopt, the type of infrared radiation that molecules absorb, and the persistence of the substance in the atmosphere.

Core Practices

Analyze data to infer patterns in the composition, structure, and properties of greenhouse gases in the atmosphere.
Develop and apply molecular models to predict and explain the outcome of interactions between different types of molecules and different types of electromagnetic radiation.
Build explanations and generate arguments about the differential properties and effects of various greenhouse gases in the atmosphere.

Systems Thinking Skills

System Composition: Identify and characterize the properties of entities in the atmosphere that absorb infrared radiation and act as greenhouse gases.
System Structure: Explore and identify interactions at the electronic, atomic, and molecular levels that affect a molecule's response to infrared radiation.
System Behavior: Infer the light-matter interactions of different substances based on their chemical composition and structure.
System Effects: Analyze the differential global warming effects of different types of substances based on their molecular structure and behavior in the atmosphere.

Socio-environmental Competencies

Recognize factors that affect the global warming potential of different greenhouse gases.
Propose and evaluate diverse strategies to reduce the emission of greenhouse gases into the atmosphere.

Design

The following presentation includes a sequence of content and activities for a proposed lesson (approximately five 50-minute sessions) that engages students in the development and application of chemical systems thinking to the understanding of greenhouse gases in the atmosphere. The lesson is designed for an introductory general chemistry lecture course at the university level.

Greenhouse Gases.pptx

This example lesson introduces and applies the following chemistry concepts: Electronegativity, partial charge, bond polarity, molecular polarity, light-matter interactions, and IR active vibrations.
This example lesson assumes students already have a basic understanding of the particulate model of matter, atomic structure, molecular structure, and basic properties of electromagnetic radiation.
The following diagram depicts a suggested schedule for the implementation of this example lesson:

The example lesson includes a set of interspersed activities (labeled "Let's Think") that students are expected to complete in small collaborative groups and then share their ideas in whole class discussions. These activities ask students to share and explore chemical concepts, actively engage in core science practices like analyzing data, making predictions, applying models, and generating explanations, and practice systems thinking skills. The specific system thinking skills that each activity may help foster are highlighted using representative icons. They also create opportunities for the instructor to formatively assess student learning and provide specific feedback to advance their understanding.

Map Out

During the "map out" phases of a lesson, students are introduced to the socioenvironmental problem under analysis to identify the systems in interaction. This phase should allow them to develop an overall view of the nature and complexity of the problem or phenomenon to be analyzed. As illustrated in the example lesson on greenhouse gases, this can be accomplished by engaging students in activities that ask them to analyze the emission spectra of the Sun and our planet and use their prior knowledge to build an initial system map identifying possible components of the chemical systems under analysis and their interactions. These activities seek to create a need to know and opportunities for students to activate and share prior knowledge and experiences related to the phenomenon.

Zoom In

For example, in the proposed module on greenhouse gases, students identify important atmospheric components, such as O2, N2, CO2, and H2O, and explore properties that affect their interaction with electromagnetic radiation. For this purpose, students are introduced to the concepts of bond polarity and molecular polarity and use an interactive tool to infer the polarity of different chemical entities in the atmosphere:

Later in the lesson, students explore how bond and molecular polarity determine whether molecules absorb infrared radiation, and thus may contribute to global warming:

Zoom Out

Once students model and understand the phenomena of interest at submicroscopic levels of granularity, it is important to "zoom out" using activities that help them recognize system-level properties and behaviors that emerge from the interactions between components. For example, in this phase of the proposed lesson on greenhouse gases, students are asked to analyze the emission spectra for the Sun and Earth in combination with the absorption spectra of H2O and CO2 to infer consequences for our planet:

Connect

In the "Connect" phases of the lesson, students engage in activities that allow them to explore the effects of interactions between relevant subsystems, as well as apply their knowledge in making decisions and suggesting individual or collective actions directed at addressing the societal and/or environmental problem under consideration:

Evaluate

The "Let's Think" activities interspersed in the example lesson create diverse opportunities to formatively assess student learning and provide specific feedback to advance their understanding to meet the lesson's learning objectives. These activities also help students evaluate strengths and areas needing improvement in their learning. As part of the summative assessment, we suggest implementing an activity that requires students to apply their understanding to analyze a different system of interest. This summative assessment could be completed individually or in small groups, inside or outside the classroom. An example of this type of summative assessment is included at the end of the example lesson as a "Let's Apply" (LA) activity focused on the analysis of less commonly known greenhouses in our atmosphere:

Reflect

During the implementation of the lesson, we must systematically gather information about student learning and performance that can help us critically reflect on aspects of the lesson that need to be modified to support student learning of the central ideas, core practices, and socio-environmental competencies targeted by the lesson.