Particle diagrams of water | Johnstone’s triangle

Learning objectives

1. Describe macroscopic properties of water as solid, liquid and gas.
2. Draw particle diagrams to represent solids, liquids and gases.
3. Explain differences between solids, liquids and gases using particle diagrams.

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 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. 

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

When introducing a topic, do not try to introduce all of the levels of thinking at once. This will overload working memory. Instead complete the triangle over a series of lessons, beginning with the macroscopic level and introducing other levels, in turn, once secure.

All of 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

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