Chemistry is difficult to learn. Walk into any chemistry classroom, and you’ll be soon confronted with many abstract concepts. Abstract ideas have no physical form, and as a result, they are difficult to understand. Topics like the mole, quantum numbers, and the atom are tricky to comprehend unless they are related to something more concrete.
An analogy serves the purpose of bridging an abstract idea to familiar knowledge, and there are many favorites in chemistry education.
- A recipe for baking a cake can be used to grasp stoichiometry.
- Familiar units like the 'dozen' help students understand the mole.
- Preparing ‘smores’ (a classic campfire treat) aids comprehension of limiting reactants (see image 1).
Image 1: Students understand limiting reactants better with an analogy like 'smores.'
What Is An Analogy?
Simply stated, an analogy is a comparison between a familiar domain of knowledge and one that is not. The familiar domain is commonly referred to as the “analog,” and the “target” represents the unfamiliar. An analogy is used effectively when the knowledge held in the familiar domain is transferred to the unfamiliar domain, making it easier to learn.1
Figure 1: The features of an analog are used to comprehend the target.
In a previous post, I provided a brief overview of pedagogical content knowledge (PCK), a unique form of teacher knowledge.2,3 As a component of PCK, analogy use is a specialized teacher skill. However, teachers do not always apply analogies correctly, and misuse can actually interfere with student learning and lead to misconceptions.1
Tips for More Effective Analogies
1. Teach Students About Analogy
Analogies are common in everyday life; however, students do not necessarily know why we use them or how they work. Although students learn how to define and recognize analogies in other courses, it’s still beneficial to teach students about analogy use in the context of science - tools to access complex ideas. As an example, the solar system is a common analogy for the atom. This particular analogy is an excellent reference for understanding the purpose and limitations of an analogy. Relating the solar system to the atom helps learners understand the different subatomic particles; the planets are analogous to the electrons, and the sun is analogous to the nucleus. However, the solar system is a limited analog because electrons exist in a cloud of probability rather than a discrete orbit. An analogy is merely a resemblance of the reality, rather than reality itself. So, before using an analogy, teach analogy.4
2. Analogies Should Be Simple and Easy to Remember
Students become confused and stop paying attention when analogies are too complex or lengthy. Since it's often not until the end of the analogy that the analog-target relationship is clarified, students must remain focused for the entire explanation. Students report a preference for simple analogies because they present a comprehensible idea to which they can fall back on when information becomes more complex. Students don’t even mind if an analogy is “stupid” as long as it is easy to remember and is something they can refer back to as support for further learning.1
3. The Best Analogies Are Familiar
Ideally, analogies build on pre-existing and relevant knowledge. The more the students relate to the analog, the more effective the analogy will be. Analogies that use familiar topics and language increase the likelihood that students will engage with a difficult topic. For instance, students are three to four times more likely to pay attention to the familiar language of an analogy than to new scientific language. Furthermore, students are more interested when new information is connected to real-world experiences, especially when it impacts their daily lives.5
4. The Purpose of the Analogy Must Be Clear
Many students resort to mechanical use of an analogy, rather than a deep understanding of the target concept. This mistake often results when a student learns about the analogy without connecting the analog to the target knowledge. For instance, when asked to the describe the function of mitochondria, many students respond, “it's the powerhouse of the cell,” but they are unable to explain why this is an appropriate analogy. Adding to this problem, students who supply an acceptable analogy on an assessment are often rewarded with a correct response, even though they have not communicated a true understanding of the target. To increase its power, it's best to introduce the target concept before an analogy is used. Teach students that the analogy is not the target knowledge; rather, it's a tool to reach new knowledge.1
5. Explain the Relationship Between the Analogy and Target Concept
Many students have difficulty seeing a connection between an analog and the target concept, yet, instructors often assume that all students have the ability to make those links. Teachers frequently create their own analogies after significant contemplation of a certain concept. Consequently, they understand the relationship with the target better than anyone else. Since students are brand new to the concept, they are not able to recognize the same relationships, opening the door to misconceptions and a limited understanding of the target concept. So, prevent confusion by explaining how an analogy helps better understand the target concept.1
6. Explain the Limitations of the Analogy
Analogies never completely describe the target concept, and many students can’t identify limitations. As a result, inappropriate ideas are often applied to the target, leading to additional misconceptions. With practice, students should be able to recognize limitations for themselves. Until then, when using analogies, it's wise to point out and discuss their limitations.1
7. Use Visuals
Pictures and diagrams enhance the relationship between the analog and a target concept (see image 2). Visuals bring focus to the key aspects of the analog and make the analogy more memorable. As previously stated, abstract concepts have no physical form and as a result, they are difficult to learn. Pictures and diagrams assist learners when learning abstract ideas because they provide a concrete reference when constructing new knowledge. Chemistry is more abstract than other sciences; thus, it is necessary to use more visuals. This fact is evident by the increased use of pictorial analogies in chemistry textbooks compared to other science textbooks. An analysis of secondary science textbooks found that chemistry textbooks contained the highest level of pictorial analogies (29%) compared to an average of 16% in all science textbooks.6 Whenever the opportunity presents itself, supplement analogies with visual, especially when teaching particularly abstract concepts.
Image 2: Example of a pictorial analogy used to help learners understand activation energy.
8. Save Analogies for the Difficult and Challenging Concepts
When asked to describe situations in which analogies are not useful, students expressed that analogies aren’t necessary when concepts are “easy.” From the students’ point of view, they do not want extra, unnecessary information when they are trying to learn the important course material. On the other hand, students find analogies helpful when they are learning difficult concepts. So, save analogies for difficult concepts and help to avoid unnecessary information that could take the focus away from the course content.1
Effective analogies are vital for teaching chemistry because it is such an abstract subject. With a little extra reflection and intentionally regarding analogy use, you can prevent misconceptions and improve student learning.
Please leave a comment; I would love to hear some of your favorite analogies for teaching chemistry.
References
- Orgill, M., & Bodner, G. (2004). What research tells us about using analogies to teach chemistry. Chemistry Education Research and Practice, 5(1), 15-32.
- Shulman, L. S. (1986). Those who understand: Knowledge growth in teaching. Educational researcher, 15(2), 4-14.
- Shulman, L. (1987). Knowledge and teaching: Foundations of the new reform. Harvard educational review, 57(1), 1-2.
- Brown, S., & Salter, S. (2010). Analogies in science and science teaching. Advances in Physiology Education, 34(4), 167-169.
- Lemke, J. L. (1990). Talking science: Language, learning, and values. Ablex Publishing Corporation, 355 Chestnut Street, Norwood, NJ 07648 (hardback: ISBN-0-89391-565-3; paperback: ISBN-0-89391-566-1).
- Curtis, R. V., & Reigeluth, C. M. (1984). The use of analogies in written text. Instructional Science, 13(2), 99-117.