• The concrete (or material) mode is three-dimensional and made of resistant materials, e.g., a plastic ball-and-stick model of an ion lattice, a coloured plastic model of the human circulatory system, a metal model of an aeroplane.
• The verbal mode can consist of a description of the entities and the relationships between them in a representation, e.g., of the natures of the balls and sticks in a ball-and-stick representation, of veins and arteries, of the parts of a model aeroplane. It can also consist of an exploration of the metaphors and analogies on which the model is based, e.g., ‘covalent bonding involves the sharing of electrons’ as differently represented by a stick in a ball-and-stick representation and in a space-filling representation. Both versions can be either spoken or written.
• The symbolic mode consists of chemical symbols and formula, chemical equations, and mathematical expressions, particularly equations, e.g., the universal gas law, the reaction rate laws.
• The visual mode makes use of graphs, diagrams, and animations. Two-dimensional representations of chemical structures (‘diagrams’) fall into this category as do the ‘virtual models’ produced by computer programmes.
• Lastly, the gestural mode makes use of the body or its parts, e.g., the representation of the movement of ions during electrolysis by means of pupils moving in counter-flows.