What does watching a parachuting team free-falling through the sky have to do with teaching the particle nature of matter to your elementary or middle school students, or with helping your secondary or first-year university-level students learn about structure and bonding? If you are an elementary teacher, perhaps you use a learning sequence that begins with showing round spheres of different colours that represent the particles that make up everything around us. If you adopt common practice as a high school or first-year university teacher, you might introduce bonding in molecules by asking your students to learn the rules of VSEPR and hybridization theories. Common practice is to introduce the theoretical explanation of the particle nature of matter before empirical observations of the properties of different states of matter, and theories of bonding before evidence for experimental geometries. Often such explanations do not include overt discussion of the nature and complementarity of different theories and models to explain experimental evidence.
Do the sequences and approaches to introducing the particle nature of matter or structure and bonding matter? As a result of these common sequences for presenting theories and concepts, and sometimes because of explicit language that conflates models of reality with reality, students often develop misconceptions. Elementary students may develop naïve realistic understandings that lead them to believe, for example, that aluminum atoms that make up a pop can are actually made of grey spherical balls. Secondary or first-year university students may come to believe that carbon atoms in molecules of alkanes are tetrahedral because they are sp3 hybridized. Assessment questions at secondary or post-secondary levels often ask students to list “the hybridization” of certain atoms in molecules, or their “VSEPR geometries” without overtly referencing hybridization and VSEPR geometries as powerful but limited models for making sense of experimental data.
An entrenched practice in chemistry education is to introduce challenging concepts such as the particle nature of matter or the nature of bonding through a flow of ideas that starts with concepts and theories to be learned — often presented in isolation from the evidence that underlies those facts and then moves to applications of those concepts. Not only can students easily develop misconceptions as a result, but they are left with understandings of the nature of science that do not authentically represent the way humans work to develop scientific ideas that change over time. Getting the flow of ideas right matters, because students’ understanding about the nature of science will influence their attitudes toward learning chemistry and their ability to react thoughtfully and critically to scientific claims. Deep understanding of science, including chemistry, requires understanding the evidence for theories and the nature of models to explain that evidence.
So what does all of this have to do with free-falling parachuters? In new interactive visualizations created by the research team at the King’s Centre for Visualization in Science, we make use of learning sequences and approaches at both the elementary and secondary/post-secondary levels that we believe provide more authentic introductions to the nature of science, and which eliminate the need to tell students at upper levels when confronted with more complex data, that what they had learned at introductory levels is wrong.
In a newly released and freely accessible interactive set of resources for students ages 10 – 15, we introduce the particle nature of matter concurrently with discussion of complementary models in science and after engagement by students with observations about liquids, solids and gases. Students are invited to understand those observations at the macroscopic level and develop molecular level explanations that are “good enough” to explain the observations. Depending on what properties of substances are being explained, “good enough” models for particles might be Lego® building blocks, fuzzy squares or spherical balls of different colours. Students are invited to assess whether dancing leprechauns might be “good enough” models to explain the motion of particles in different phases. And a parachuting team free-falling, and forming patterns in the air that break apart and re-form, might be a “good enough” model to explain some features of what happens when new substances are formed in chemical reactions, where small unseen particles break apart and join together in new ways.
At the secondary or first-year university level, a more authentic view of how chemists arrive at their understanding of structure and bonding is to start with the activity of human beings who provide experimental evidence for structure and bonding. As a teacher, you might give very simple explanations of what kinds of evidence come from infrared spectroscopy (connectivity patterns in functional groups), mass spectrometry (evidence for molecular formulas), X-ray crystallography (bond lengths and bond angles) and NMR spectroscopy (map of the C-H framework of organic compounds), and then convey a sense of how chemists imagine complementary scientific models to explain that evidence. Such a sequence can help students see both the power and limitations of models; the imaginative and creative processes that lead to robust explanations; and to avoid equating models with reality. The term “good enough” model works just as well at this level as with elementary students, to powerfully introduce the idea of complementary models to explain evidence. Rather than teaching that certain atoms are “hybridized” or have certain shapes because of VSEPR theory, complementary “good enough” models can be introduced as needed to explain experimental evidence, starting with simple Lewis structures, VSEPR patterns, valence bond models, hybrid orbitals, and to explain certain properties — molecular orbital theory.
References and notes
The Chemistry for Ages 10 – 15 interactive resources to help elementary, junior high and high school students strap on their parachutes and imagine complementary “good enough” models for the particle nature of matter can be found.
The resources are described more fully in B. Gustafson, P. Mahaffy, B. Martin, Journal of Computers in Math & Science Teaching, Guiding Age 10 – 11 Students to Notice the Salient Features of Physical Change Models in Chemistry Digital Learning Objects, January 2015, pages 5-39.
Approaches and learning sequences to introduce structure and bonding in more authentic ways can be found in
- P. Mahaffy, Chemistry Education: Best Practices, Opportunities and Trends, Chemistry Education and Human Activity, Chapter 1, Wiley, 2015.
- P. Mahaffy, B. Bucat, R. Tasker, J. Kotz, P. Treichel,
G. Weaver, J. McMurry, Chemistry: Human Activity – Chemical Reactivity, 2nd Canadian and 2nd International Editions, Nelson Canada/Cengage, Chapter 10, 2014.
The development of interactive learning resources for Chemistry for Ages 10 -15 was supported by a grant from Canada’s Social Sciences and Humanities Research Council (SSHRC), in collaboration with Dr. Brenda Gustafson at the University of Alberta, Dr. Brian Martin at the King’s University, as well as the team of undergraduate King’s research students.
Peter Mahaffy is professor of chemistry at the King’s University in Edmonton, and co-director of the King’s Centre for Visualization in Science. He is past-chair of IUPAC’s Committee on Chemistry Education and co-author of a first-year university chemistry textbook, Chemistry: Human Activity, Chemical Reactivity.
Editor’s note
The referenced website is a great place to send students, especially grade 9 science students. It is interactive and students cannot continue unless they answer questions along the way. It leads students through eight lessons, as shown below. When you go to www.kcvs.ca, look under “Visualizations” then “Elementary Science”.
The video of “Sky Divers: a model of a chemical change” can be found in Lesson 7 — Particles and Chemical Changes. There are some “good enough” models that will help your students.
