Why Do Some Molecules Absorb Infrared Energy?

The Lawrence Hall of Science, The Lawrence Hall of Science

In this short, hands-on activity, students build simple molecular models of 4 atmospheric gases (O2, N2, C02, and methane), compare their resonant frequencies, and make the connection between resonant frequency and the gas's ability to absorb infrared radiation.

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Notes from our reviewers

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Educator should definitely include the reading in the surrounding chapter (chapter 2 of the GSS curriculum on Climate Change [link http://www.globalsystemsscience.org/studentbooks/cc/ch2] about what resonant frequency has to do with why greenhouses gases are able to absorb infrared light. This animation [link http://scied.ucar.edu/molecular-vibration-modes] provides a visual representation of molecular resonance and would be useful to use as a reference/resource in this activity . Free teacher guide with downloadable files and additional activities is available upon request at: [link http://www.globalsystemsscience.org/teacherguides].
The activity demonstrates how gas molecules in the atmosphere resonate when they are struck by vibrating photons of light energy. Molecular resonance is a key factor in the ability of greenhouse gases to absorb infrared energy. Comments from expert scientist: Addresses a very common knowledge gap in understanding the greenhouse effect, what greenhouse gas molecules do, and which molecules are (and are not) greenhouse gases. The models highlight key structural differences between the non-greenhouse gases (N2 and O2) and the greenhouse gases (CO2 and CH4). It may be helpful to have a link to the "GSS Teacher Guide for Climate Change Chapter 2," which is mentioned as a resource.
A hands-on activity for students to model how and why greenhouse gases absorb infrared energy and thus warm the atmosphere. Students build simple models of atmospheric gases and compare their resonant frequencies. This activity is one of several in a chapter entitled "What's So Special About Carbon Dioxide", in the Climate Change section of the Global Systems Science online curriculum. Teacher Guides for this curriculum are available on a Teacher Site that is accessible by contacting the developer, Alan Gould, at [link http://www.globalsystemsscience.org/teacherguides]. A basic understanding of the electromagnetic spectrum, and where wavelengths of infrared and visible light energy fall on the spectrum, is useful.
Activity is user-friendly with limited cost for reusable materials. Minimal preparation time required; educator is advised to pre-set the attachment points on the atoms (polystyrene balls) for the bonds (cable ties or pipe cleaners). Many different kinds of materials can be used to create models of molecules, but not all of them will allow user to experiment with resonance.