Representing elements and compounds | Developing understanding | 14–16 years | Resource

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Elements and compounds can be visualised using a range of diagrams, models, 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.

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A ramped worksheet to help learners develop their mental models of different representations of elements and compounds. With icons to indicate the conceptual level/s of each question.

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Learning objectives

Connect the more basic particle model representation with metallic, ionic and covalent structures.
Match element symbols to element names and appearance.
Interpret the numbers in chemical formulas as providing the ratio of atoms or ions in each compound.

How to use this resource

This resource aims to develop learners’ understanding of the different ways that elements and compounds can be represented. The questions encourage learners to think about how elements and compounds can be visualised in diagrams and through symbols and formulae and what this means at the sub-microscopic level. 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 Sulfur dioxide Johnstone’s triangle worksheet which considers the simple covalent compound and it’s release into the atmosphere to mix with other gases through the use of the particle model.

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. Or, 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. Answers can be found in the teacher notes.

The first question aims to develop learner understanding of the diagrammatic representation (a form of symbolic understanding) of elements and compounds and what they mean in terms of atoms and ions (sub-microscopic understanding). Learners are required to make connections between earlier learning about the basic particle model and later learning about metallic, ionic and covalent structure and bonding. Some learners may suggest that the main particles in a metal are positive ions (surrounded by delocalised electrons). This is not incorrect, but the basic particle diagram does not show the delocalised electrons and therefore the circles represent the whole metal atom.

Question two requires learners to recall and connect element symbols (symbolic understanding) with the name of different elements. It also shows that a symbol or formula must be used when linking to a sample of (macroscopic understanding) of different elements. This question assumes prior familiarity with common element symbols and simple formulae for diatomic molecules.

In question three learners develop understanding of the representation of compounds by chemical formulas (symbolic understanding) and what these mean in terms of ratios of different atoms or ions (sub-microscopic understanding). The ratios may theoretically be written in the opposite order, in which case these should also be marked as correct.

The final question develops learners’ understanding of the representation of covalent substances in the gas state (symbolic understanding) and shows visually how the basic circle representation used in the particle model connects to a more advanced representation of the arrangement of molecules (sub-microscopic understanding). The use of dotted circles combined with molecule diagrams aims to support learners to connect the two different representations and to develop a more advanced mental model that is needed for understanding ideas such as intermolecular forces.