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"It was the best of chemistry, it was the worst of chemistry, it was the creation of wisdom, it was the creation of foolishness …"

—A humble modification of Charles Dickens’ famous first line from A Tale of Two Cities

As any chemistry teacher knows, the central science is rife with difficult concepts, complicated models, and abstract explanations of substances that have never been seen. This complexity naturally drives teachers to find ways to simplify chemistry ideas for students. We use analogies, images, graphs, cartoons, and a variety of other resources and strategies to bring the ideas of chemistry to students in ways they can more easily grasp and comprehend. Any strategy that allows students to make sense of complicated concepts is a useful strategy. We must, however, take caution with our words to ensure that we don’t simplify concepts so far that what we say becomes wrong.

As a teacher of both first-year and second-year chemistry, I am in a position to directly evaluate the effectiveness of my first-year course by assessing the preparedness of the second-year students. At the beginning of each unit in the second-year course, I become aware of students’ misconceptions, and the holes in their understanding become apparent as they delve deeper into the fundamental topics they learned in the first-year course. This recurring phenomenon serves as a reminder to me that I must pay close attention to my words when I introduce ideas. Like most chemistry teachers I have met, I am skilled at taking complex ideas and expressing them in simple language. However, having taught second-year chemistry for a number of years, I now realize that some of my simplifications have increased students’ misconceptions rather than eliminating or reducing them. Table 1 shows two examples of oversimplifications I have made in my first-year class that led to students’ misconceptions. I’ve also included how I’ve changed my explanations to prevent this.

Table 1

Examples of misconceptions as a result of simplifications from my experience.

Observed second-year student

Mg(s) + 2 H+(aq) → Mg2+(aq) + H2(g)

When prompted to show charges for each appropriate species, students tend to make mistakes such as giving a 2+ charge to both magnesium species and writing “H2+” for one or both hydrogen species.

Apparent reason for misconception

Students are unable to recognize the difference between atoms and ions in a single replacement reaction because they are conditioned to believe that, for example, an alkaline earth metal “always” has a +2 charge. This comes from repeatedly asking students the charge of the representative element ions when they learn how to write formulas for ionic compounds.

How I’ve addressed reducing this misconception in first-year chemistry

I add language to explanations to clarify that an atom only forms the designated charge when it is an ion.

Observed second-year student

Incorrect justification for variations in ionization energy periodic trends, even though the misconception is seemingly identified and addressed when the concept is reintroduced.

Apparent reason for misconception

Students think that half-filled and filled valence shells have a “special stability” and that this stability explains the variations in the periodic trend. During lessons and conversations, students seem to understand why this is not a valid justification, but in testing situations some revert back to the simplified idea of a special stability.

How I’ve addressed reducing this misconception in first-year chemistry

I eliminate the idea of filled and half-filled orbitals having any special stability. I explain that the attraction an atom has for its valence electrons is a net effect of proton and electron interactions within the atom. I also explain that atoms make the rules and we try to make sense of them—when a trend doesn’t fit an established pattern, students should look for ways to explain the discrepancy.

There are many ways that simplification can lead students astray. The first example in Table 1 shows that in an attempt to make a specific skill easier for first-year students (patterns of charges for ions), I unintentionally led them to generalize the assignment of charges to all situations, thus confusing the concept I was attempting to strengthen in the later class. The second example shows how a simplified phrase (special stability) intended to gloss over the bigger ideas turned into a memorized fact, even when further explained and addressed in the second-year class.

Tell the full story

Younger children often repeat words out of context that can be interpreted as either alarming or hilarious, because much of a child’s life involves learning by imitation. Though older children develop other methods of learning throughout their schooling, the second example in Table 1 shows that there is still a tendency for high school students to occasionally revert to imitation as a learning technique. I have certainly heard my own students parrot my words while working through a problem or when helping another student. My students’ propensities for imitation show me that I must be careful in choosing my words. Before discussing these difficulties with students in an attempt to understand their barriers to learning, I hadn’t really considered the effects that my simplifications may have on their future mindsets.

For example, a few years ago my AP Chemistry class was learning about polar molecules. They were specifically focused on learning about structural aspects of molecules that might affect the magnitude of a dipole moment. One of the students said, “But last year you said that the lone pairs don’t affect the polarity.” Yes, I said that. Oops … time to backpedal! This was neither the first nor the last time that I was “caught” telling students something in first-year chemistry that I would completely reverse in second-year chemistry. I eventually began to hear myself say things during my first-year courses and then immediately think of the argument that a student would give me the following year when diving further into the same topic.

The second-year students began to jokingly accuse me of “lying” to them during their first year and only revealing the real story during the second year. This is when I realized that “telling the truth” from the beginning might be a good idea. Initially, the arguments against this idea were that the students were too inexperienced to make sense of it or that it wasn’t necessary to dig that deeply during a first-year course. Over time, however, I have come to realize that my students benefit when I expose them to chemically accurate concepts from the beginning, rather than simplifying to the point where I contradict what will be learned in a future chemistry course.

Developing critical thinkers: The tale of two chemistries

Many television advertisements feature stories of a seemingly insignificant event that triggers a comedic string of calamities. Though perhaps not as comedic as the commercials, the cartoon below (Figure 1) shows an exaggerated set of parallel stories that I have developed with the intention of showing, like the light-hearted commercials, that the effects of our teaching today may have implications far beyond our students’ next courses.

In the top-row chemistry class, the student is given accurate information, simplified enough for them to understand, but not so simplified that it hampers her ability to critically think about the concepts. In the bottom-row chemistry class, the student is given oversimplifications, which leads, in the cartoon, to a lack of ability to think about what she is learning.

Certainly I do not mean to imply that we can promote critical thinking merely by avoiding simplification. I do, however, believe that if we are not careful and thoughtful in our simplifications, they may compromise our students’ abilities to think deeply about the topics related to those simplified ideas. Certainly, memorization of simple facts has its place, but in a course filled with opportunities for critical thinking, we do the students a disservice if we don’t foster this type of thinking every chance we get.

I believe that we can be chemically accurate about very complex topics without having to teach graduate-level chemistry. I see no harm in telling students that you are giving them a simplified model that is not strictly true so they can understand how to start thinking about atoms and molecules. For example, over the past few years of teaching bonding principles, I have found myself repeating that we are only examining the simplest models using examples that are easy to classify and that there is really a lot more variety to the possibilities. Even this simple reminder is useful because it helps students realize that scientists use models and patterns to help make sense of things but that those models and patterns are never a perfect representation of the real thing. Pretending that atoms and molecules can be characterized into only two or three perfectly defined boxes may lead students to close their minds to other possibilities and decrease their ability to critically think about what they are learning.

Though the examples I use in this article are all related to bonding, there are opportunities for critical thinking and chances that students will develop misconceptions in any chemistry unit. I hope that my musings will encourage you to examine your simplifications and consider whether you are facilitating deeper thinking in students or inadvertently doing the opposite. Like the duality implied in the opening lines of Charles Dickens’ A Tale of Two Cities, our methods of simplifying concepts can be both wise and foolish.

Which chemistry tale will you teach?


  • Figure 1 was created by the author.
  • The metaphor in this article was inspired by the first lines of Charles Dickens’ 1859 novel, A Tale of Two Cities.


Thanks to Virginia M. Grossman, superintendent of Westampton Township Public Schools, for suggestions and edits, and for thinking of Charles Dickens when I first told her my ideas for this article.