Students can find the particulate state of matter difficult to conceptualise and model. Later on, they have to draw conclusions from structure-properties to microscopic properties, which they also find difficult.

It is well known from the literature that many students expect air or water to be between particles rather than nothing between particles. So the perspective on holes in this unit particularly highlights the emptiness in between matter and confronts them with the “horror vacui”. It is also well documented that students transfer microscopic properties onto particles. When a coloured solution is seen – what is causing the colour? Linking colour to the molecule can therefore be difficult for students.

Possible arguments to explain observations will be based on ‘colour’, imperfections in the membrane, density, mass of particles. Discussion (and further experiments) will counter these arguments.

Linking molecular structure to macro properties can be difficult for students. Subunit 2 and 3 can therefore be helpful as properties of polymer films are changed, e.g. to be dependent on the amount of plasticizers added or the pH of a solution added to a superabsorber. Hence, the structure of the polymer must be different.

By analyzing structure-property-relations, students also have to combine experimental observations with model-based explanations. The role of models as essential addition to experiments could be highlighted to form a better understanding of the nature of science and inquiry-based approaches.