Using Analogies to Teach Chemistry Concepts

Chemistry is often a difficult subject because of its abstract nature, which requires students to understand scientific concepts that are not visible to the naked eye. Visualizing what is happening at the molecular level can be very difficult, especially for concrete thinkers. One helpful strategy is using analogies to make concepts accessible and relevant.

A brief review of available research on using analogies to teach secondary chemistry reveals many studies in countries around the world going back several decades. Recent research suggests that analogies can be helpful for learning new and unfamiliar concepts if properly chosen and presented but that teachers should also be mindful of the limitations of teaching with analogies.

Early in my career, I often used an analogy of peer relationships to teach intermolecular forces or weighted averages for grades to teach atomic mass; however, I realized that a number of students didn’t seem to make any connection between the analogies I used and the chemistry concepts I was teaching. They could talk about the analogy itself, but they had no idea how it related to what I was teaching. I began researching the topic and found material emphasizing the importance of making explicit connections between the analogy and the chemistry concept. This led me to revise my strategy to explicitly explain how the structure and relationships in the analogy were similar to the structure and relationships in the chemistry concepts.

The following sequence of steps is suggested to assure successful use of analogies:

1. Identify a chemistry concept.
2. Identify a real-world analogy familiar to your students.
3. Develop an activity to interact with the analogy.
4. Have students explain and apply the analogy.
5. Introduce the chemistry concept.
6. Make connections between the two explicit.

When I choose an analogy to use to teach a concept, I think about real-world situations that exhibit the same relationship or structure as the chemistry concept I want to teach and that make logical sense to explicitly explain the connection to the chemistry concept. Before incorporating the analogy into the lesson plan, I make sure that the topic is familiar to my students through firsthand experience.

Classroom Examples

Bus routes: A critical point in the sequence is identifying an appropriate real-world analogy. The analogy must be familiar and accessible to your students. If students struggle to understand the analogy, it won’t be helpful for understanding the chemistry concept.

I once used a bus analogy with a group of students in an urban setting to understand the mole as an intermediate step in unit conversions. These students used public transportation daily and knew when and how to use the transfer center. I presented a scenario where I needed to take the bus (an unfamiliar activity for me) to get from school to the car repair shop, stating that I wanted to take a direct bus because I was nervous about transferring buses. The students, who were very experienced with the bus system, explained that there was no direct route and I had to go downtown to transfer.

I then used that parallel structure of going through “Moletown” when converting units. It worked for them because they were completely familiar with the bus transportation system in the city, and the transfer station was a regular part of their lives.

I no longer teach in that district, but instead in a tiny rural district where most students walk to school, and the only buses familiar to them are school buses. The bus analogy would not be meaningful to them because they don’t use public transportation in their daily lives. If the analogy must be explicitly taught, it’s probably not a good one to use with that group. The analogy should be something familiar to them so they understand the structure and function of the situation. An innate understanding of how the analogy works is critical to successfully using the analogy to understand the parallel chemistry concept.

Baking a cake: When designing an activity to access the analogy, keep it brief but long enough for the students to demonstrate understanding of the analogy. I have students use cake mixes as an analogy for mole ratios. A 10-to-15-minute small group activity developing a written equation for baking a cake based on the box instructions is long enough to engage with the analogy to demonstrate understanding.

I can quickly assess their ability to use the structure of the analogy by asking questions about scaling the recipe up or down (how many eggs are needed to make two cakes?). This gives students confidence while proving to me that they understand the analogy. If there is confusion or lack of understanding, you can revise the plan and not spend time trying to use an analogy that isn’t meaningful to your students.

Bringing in Chemistry

Once students demonstrate understanding of the analogy focused on the relevant structure or function, introduce the chemistry concept. I generally do not even talk about chemistry until this point because the unfamiliar chemistry concepts can cause anxiety. Allowing students to interact with the analogy first lets them feel confident about a topic that they are familiar with. When introducing the chemistry concept, I point out that the concept is very similar to the analogy they just explored and remind them that they just showed understanding of the concept behind the chemistry. Now all that is needed is to associate new terminology with concepts.

In the example of cake mixes, I write the agreed-upon cake recipe equation on the board, then write an example chemical reaction underneath and ask students to identify similarities. Pretty quickly they make the connection that measurements are like coefficients, and ingredients are like substances. They notice that just like scaling a recipe up or down, they need to double or triple or halve each of the “measurements”—now using the terminology of “coefficient”—to scale up or down.

When the chemistry gets overwhelming, have students think back to the analogy to relieve the feeling of intimidation and reinforce the conceptual understanding. By being able to refer back to the familiar analogy where they were confident in explaining relationships, students can make connections and build understanding of new and unfamiliar concepts. The more connections made between the familiar and the abstract, the more confident students become.