Sulfur dioxide | Johnstone’s triangle

The particle model can be extended to explain why molecules of sulfur dioxide mix with the air in the atmosphere.

Learning objectives

1. Give two ways in which sulfur dioxide is released into the atmosphere.
2. Use the particle model to explain why sulfur dioxide molecules mix with the molecules of other gases in the air.
3. Connect the particle model representation to the arrangement of sulfur dioxide molecules.

How to use Johnstone’s triangle

Use Johnstone’s triangle to develop learners’ thinking about scientific concepts at three different conceptual levels:

• Macroscopic – what we can see. Think about the properties you 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.

For learners to gain a deeper awareness of a topic, they need to understand it at all three levels.

When introducing a topic, don’t try to introduce all three levels of thinking at once. This will overload working memory. Instead complete the triangle over a series of lessons, beginning with the macroscopic level, then symbolic and then sub-microscopic.

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.

Scaffolding

Share the structure of the triangle with learners prior to use. Tell them why you are using it and how it will help them to develop their understanding. Use an ‘I try, we try, you try’ approach when introducing Johnstone’s triangle for the first time.

More resources

To further develop learner’s thinking in all areas of Johnstone’s triangle, try our Developing understanding of representing elements and compounds worksheet. This includes icons in the margin referring to the conceptual level of thinking needed to answer the question.