Atoms and isotopes of hydrogen | Johnstone’s triangle

With this resource, learners compare an ice cube of ‘heavy water’, containing the hydrogen isotope deuterium, with standard ice. They consider the symbolic representation of different isotopes using atomic symbols

Learning objectives

1. Determine the number of protons, neutrons and electrons in an atom from the atomic symbol.
2. Recognise similarities and differences in the number of protons, neutrons and electrons between atoms and their different isotopes.

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.

Next steps

To further develop learners’ thinking in all areas of Johnstone’s triangle, try our Developing understanding of atoms and isotopes worksheet. These include icons in the margin referring to the conceptual level of thinking needed to answer the question.