How important is it for students to be able to move between chemical representations to grasp fundamental chemical concepts and phenomena?

An image showing a salt shaker; NaCl symbols and multiple lattice structures of sodium chloride are coming out of it

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A new study reveals that students of all ages have difficulties moving between the multiple representations of chemical concepts

In chemistry, we study phenomena that are difficult to directly perceive by human senses, such as the interactions between atoms, molecules and ions. To explain these phenomena, chemists have invented specialised ways to represent them, such as molecular formulas, chemical equations or molecular models. So students need to navigate three levels of representation to fully understand fundamental chemical concepts and phenomena: macroscopic, sub-microscopic and symbolic. This is known as Johnstone’s triangle.

A new study from researchers at the National and Kapodistrian University of Athens examined both secondary school and undergraduate students’ understanding of four basic chemical concepts: chemical element, chemical compound, solid state of matter and aqueous solution. Significantly, it focused on the students’ competence in moving fluently between the three different levels of chemical representations.

Travelling around Johnstone’s Triangle

The researchers conducted their study in two phases. The first involved a multiple-choice questionnaire, consisting of real pictures (macroscopic), molecular formulas (symbolic) and sub-microscopic diagrams, and asked students to select an equivalent representation at a different level. This was followed by a semi-structured interview to uncover more detail.

Many already known alternative conceptions were identified, but this research uncovered several new alternative conceptions. For example, many students believed that the metallic property of a material results from the presence of a separable component that imparts the metallic property.

The results suggested that the school students had a limited ability to move between chemical representations. Unsurprisingly, the undergraduate students performed better. However, their performance was not considered satisfactory, given their level of education. Both the school students and undergraduates performed worst when translating sub-microscopic representations of chemical compounds to equivalent symbolic representations. The results revealed that, even after significant training in chemistry, students still have difficulties understanding chemical representations.

Teaching tips

As teachers, we are able to switch back and forth between different levels of representation with ease. Indeed, we may even do it without realising it. We need to be explicit in how we teach representation-heavy concepts to avoid any student confusion.

  • Use multiple representations for the same concept as often as you can, highlighting the similarities, differences and deficiencies between them.
  • Explicitly teach concepts where alternative conceptions are known, such as where the same chemical symbols can be used for both the macroscopic and sub-microscopic levels, such as where H2 is used to represent a single molecule as well as a substance.
  • Allow students the opportunity to practise moving from one representation to the other, and to practise that translation in reverse too. The results of this study indicate that students’ ability to translate a representation from one level to another does not mean they can perform the reverse translation.
  • Emphasise the translation of sub-microscopic representations of chemical compounds to equivalent symbolic representations. The study also highlighted this as a particular challenge for undergraduate students.
  • Consider tackling representations early in your science curriculum, for example when the particle model is introduced, to ensure that alternative conceptions do not take root early.
  • Use questions that ask students to translate from one level of representation to another as a tool to promote meaningful understanding, but also to elicit students’ alternative conceptions.
  • The appendix of this study contains many examples of relevant questions. Use these directly, or can use them to create your own questions.