Developing understanding of atoms and isotopes

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

Learning objectives

1. Recall the types of subatomic particle, their location in an atom and how to determine the number of each from the atomic number and mass number. Distinguish an atom from an ion when given numerical information about the number of protons and electrons. 
2. Determine the number of protons, neutrons and electrons in an atom from the atomic symbol. 
3. Recognise similarities and differences in the number of protons, neutrons and electrons between atoms and their ions and different isotopes. 
4. Determine the atomic symbol for different isotopes using information about the number of protons and neutrons.

This resource aims to develop learners’ understanding of isotopes and how they are represented. The questions encourage learners to think about similarities and differences in the number of different subatomic particles in a range of atoms, ions and isotopes. 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 Atoms and isotopes of hydrogen Johnstone’s triangle worksheet which guides learners to think about the difference between hydrogen and the deuterium isotope, including a comparison of ’heavy water’ and normal ice cubes, 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.

Give learners physical models to use and manipulate, such as a Molymod™ kits or counters.

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.

Answers and guidance

There are four multi-part questions in the student worksheet. The first question consolidates learners’ understanding of the location and number of each type of subatomic particle in an atom (sub-microscopic understanding). Question 2 develops learners’ ability to interpret atomic numbers (symbolic understanding). 

Question 3 develops learners’ understanding of similarities and differences in the number of protons, neutrons and electrons in atoms and their ions and in different isotopes (sub-microscopic understanding). The final question builds learners’ confidence in distinguishing isotopes of the same element from an isotope of a different element using information on the number of protons and neutrons (sub-microscopic understanding).