Roaming the representations

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.