Drawing boosts understanding

Many chemical concepts can be represented in more than one way, each providing different information. For example, the structure of a molecule can be represented as a formula, a 2D structural drawing, a ball-and-stick model or a space-filling model. These multiple representations are often a source of confusion for students.

Multiple representations

In some cases, we present students with preconstructed diagrams to interpret. These can be of scientific equipment to support practical work, for example, or particulate-level diagrams to help students link the macroscopic and sub-microscopic domains.

When students create diagrams themselves, it promotes the development of observational and reasoning skills. This can develop their mental models of science phenomena as they need to select key spatial features and represent them in a visual form. The development of these skills can be used as a means of assessment.

While challenging, the use of multiple representations is beneficial to students. Each form has different characteristics that convey complementary information about a concept. Drawing diagrams helps students to construct, organise and communicate their understanding of these concepts. They can then navigate the challenge of accumulating fragmented knowledge, develop problem-solving strategies and construct a deeper understanding of complex science concepts.

The challenge of multiple representations is considerably greater when there are many different fundamental chemical concepts needed to explain another – the concept of hydrogen bonding in water, for example. How do you encode information about electronegativity, molecular shape, molecular orientation and lone pairs of electrons into a single diagram that forms a coherent explanation?

A new study by researchers from Australia and Taiwan answers this question. In it, they use student-generated diagrams to investigate students’ conceptual understanding of the nature of hydrogen bonds between water molecules in snowflakes.

An intermolecular challenge

The researchers used a series of scaffolded prompts to interview first and second year university students. These prompts slowly reminded students of the idea of hydrogen bonding in a snowflake, and built up to an explicit prompt to illustrate a system of multiple hydrogen-bonded water molecules in a diagram.

The diagrams from 60 of these interviews, and interview transcripts, were analysed using an inductive approach, generating different categories relating to the students’ conceptions of hydrogen bonding in a snowflake. The analysis exposed several difficulties that students face, and new alternative concepts about hydrogen bonding.

Most students were able to adequately represent the bent structure of a water molecule in their diagrams and indicate the covalent nature of the intramolecular bonds. However, the diagrams revealed that students conceptualised the intermolecular hydrogen bonds in different ways.

Student-generated drawings were successfully used to interrogate students’ conceptual understanding

Half of the students’ diagrams illustrated the concept of a hydrogen bond correctly, including evidence of it being intermolecular, electrostatic and directional. However, the other half revealed alternative conceptions about the structure of water, the nature of intermolecular interactions and the specific involvement of lone pairs of electrons. For example, some students’ diagrams suggested that the oxygens of two different water molecules could hydrogen bond to the same hydrogen.

Other students’ diagrams suggested that both lone pairs of electrons on oxygen could collectively participate in a single hydrogen bond, without the need for precise directionality.

Even the diagrams which illustrated a sound understanding of hydrogen bonding showed that students struggle to represent molecular interactions in 3D. Hydrogen bonding is an abstract concept which is fundamental in chemistry. A coherent understanding depends on a good understanding of molecular shape, electronegativity and the distribution of electrons in molecules. So the researchers successfully used student-generated drawings about hydrogen bonding in snowflakes to interrogate the students’ conceptual understanding.