Developing understanding of symbols and formulas

Developing understanding is a series of resources that encourages learners to connect their thinking at the macroscopic, sub-microscopic and symbolic levels.

Learning objectives

1. Recognise that chemical symbols are based on the element name in English or in Latin.
2. Determine the number of each type of atom in a molecule from a chemical formula.
3. Interpret the meaning of a chemical formula representing a substance made up of separate molecules.
4. Interpret the meaning of a chemical formula representing a substance made up of one giant molecule.

How to use this resource

This resource aims to develop learners’ understanding of symbols and chemical formulas. The questions encourage learners to think about what is represented by the chemical formula of a substance made of individual molecules. This leads to the idea of a chemical formula as showing the ratio of different types of atom in the bulk substance. As a result, learners should develop more secure mental models to support their thinking about this topic.

• When to use? Use after initial teaching or discussion of this topic to develop ideas further. You can also use as a revision activity.
• Group size? Suitable for independent work either in class or at home. Or use the questions for group or class discussions.
• How long? 15–30 mins

Johnstone’s triangle

Johnstone’s triangle is a model of the three different conceptual levels in chemistry: macroscopic, symbolic and sub-microscopic. You can use Johnstone’s triangle to build a secure understanding of chemical ideas for your learners.

Introduce learners to Johnstone’s triangle with our C, O and Co Johnstone’s triangle worksheet which guides learners to think about the differences between carbon monoxide and cobalt at a macroscopic, sub-microscopic and symbolic level.

Johnstone’s triangle and this resource

The icons in the margin indicate which level of understanding each question is developing to help prompt learners in their thinking.

• Macroscopic: what we can see. Think about the properties that we can observe, measure and record.
• Sub-microscopic: smaller than we can see. Think about the particle or atomic level.
• Symbolic: representations. Think about how we represent chemical ideas including symbols and diagrams.

The levels are interrelated, for example, learners need visual representation of the sub-microscopic in order to develop mental models of the particle or atomic level. Our approach has been to apply icons to questions based on what the learners should be thinking about.

Questions may be marked with two or all three icons, indicating that learners will be thinking at more than one level. However, individual parts of the question may require learners to think about only one or two specific levels at a time.

Support

This worksheet is ramped so that the earlier questions are more accessible. The activity becomes more challenging in the later questions. You can give extra explanations for the more challenging questions. If completing as an in-class activity it is best to pause and check understanding at intervals, as often one question builds on the previous one.

It is useful for learners to observe macroscopic properties first hand. You could circulate examples of substances in the classroom, run a class practical of a chemical reaction or show a teacher demonstration of properties.

Additional support may be needed for any learners still lacking in confidence in the required symbolic representation, for example by sharing and explaining a diagram or a simulation that can show movement of the particles.