Simple Activities to Integrate Particle-Level Diagrams

There have been many conversations within the Chemistry Education community surrounding the revisions to the AP curriculum.  Twitter has been buzzing with instructors debating how to implement the changes, conferences and workshops have participants deconstructing the data from last year’s exam, and classroom teachers are working diligently to prepare their students for this year’s test. 

One way the College Board has tried to shift the AP curriculum away from algorithmic problem solving and toward more meaningful conceptual understanding is through the use of particle diagrams.  As a modeler I was thrilled to see the new emphasis on using particle-level representations to explain chemical phenomena.  This is one of the foundations of the modeling paradigm and we start drawing particles in the first week of class in first year chemistry.  My AP students would have been shocked if we hadn’t drawn particles in the advanced course.  Particle-level diagrams are so ingrained in my students as part of how we talk about chemistry that they construct them without question.  When appropriate, we approach a problem by considering, “What are the particles doing that would cause this __________?” or “Can we draw particles to illustrate why ___________ happened?”  It was clear to me that training students to think about these particle interactions as they build the foundation for their understanding of chemistry was beneficial in their more advanced studies of the subject. 

If you are a teacher looking to include more of these representations in your classroom, where can you begin?  I can share a few of the examples we’ve completed so far this year.  The demonstrations and labs are not unique to the modeling curriculum, and are found in most first year courses.  We simply add on the task of particle drawing to help student explain their understanding of what they’ve observed and to help build the model of matter we are studying in class. 

Observations of three states of matter:

The students observe the three phases of water to compare characteristics such as density, fluidity, and rigidity.  After describing the three phases in class discussion, students should offer explanations of these differences by preparing particle diagrams on whiteboards that would support their observations.  Students can compare their drawings and come to consensus and the best explanation of their observations1.

 


 

This is one of the simplest drawings, yet content rich.  My students observed water in three states as ice melts on a hot plate.  Notice the “whooshies” (the tails on the particles) indicating greater motion on the warmer gas as compared to the solid and liquid.  Also, density is correctly represented as a volume of a gas contains fewer particles and therefor has less mass than an equal volume of liquid or solid.  (This group even recognized ice floats in water and used that observation to correctly illustrate comparative densities of solid and liquid water). 

Introduction to air pressure:

Most high school texts describe pressure as force per unit area as well as provide an explanation of atmospheric pressure.  These usually include particle diagrams that show “snapshots” of particles in a box moving around in random thermal motion.  While this approach does touch the basic concept, we recommend starting by probing students’ ideas about “suction”; i.e., by asking students how they draw a liquid through a straw from a cup into their mouth. There is likely to be some hesitance on their part as they try to provide an explanation in terms of the motion of particles. It’s not difficult to convey the idea that when you suck on a straw, you are removing some of the particles of air in the straw.  Since there are more particles of air striking the liquid in the cup than are striking the liquid in the straw, the effect of these extra collisions is to push the liquid up into your mouth; there is no "suck force” that pulls the liquid up the straw1.


Have you ever ask your students how a straw works?  We had this discussion at the beginning of the unit on gases in order to help them understand the meaning of air pressure.  The student groups used the whiteboards to sketch and reason out different theories before eventually landing on the idea represented above.

Investigating the gas laws:

Using Vernier2 equipment, students collect data to determine how varying volume, amount of gas, and temperature will affect the pressure of a gas.  Students graph the data and then construct whiteboards to communicate their findings to the class. 

Following the lab, each lab team prepares a whiteboard to present their results to the class for discussion.  The presentations should include their graph (a data table is redundant), their mathematical relationship, particle diagrams at three different points on the graph, and their verbal description.  The class results should be compared and consensus reached on the best description of how the number of particles, temperature, and volume affects the pressure of a gas1.


  

  

These two sample whiteboards show the relationships between pressure and amount of gas (n) and pressure and volume.  The particle diagrams illustrate volume (size of the box drawn), amount of gas (number of particles drawn), temperature (motion lines on particles), and pressure (collisions or bounces with the container).  

The activities described here are simple ways to have students practice the skill of drawing particle diagrams.  By emphasizing the importance of accurate, clean, and deliberate diagrams early in the study of matter, progressing to using these illustrations for more complex ideas will be less daunting for students.  

Have you started using particle diagrams in your courses?  What have been your challenges or successes?

 

1.  American Modeling Teachers Association. Teachers Notes for Unit 2:  Energy and States of Matter Part I. 2013

2.  Vernier Software & Technology.  http://www.vernier.com/ (accessed October 2014).