Introducing particle models | 11-14 years

By interpreting diagrams on cards that show representations of particles, students reinforce their understanding of the terms mixture and pure substances (elements and compounds). They explore the use of models, including three-dimensional models.

The cards may be used at different levels of sophistication. For example, compounds are seen as made up of two or more different types of particles, but in a given compound the ratio of these is always the same.

Learning objectives

Students will be able to explain that:

• Substances are made up of tiny particles.
• Differences between mixtures and pure substances can be modelled using particles.

Sequence of activities

Mixtures or pure substances?

Give each student a copy of the worksheet ’Mixtures or pure substances?’. Ask students to:

1. Work in pairs.
2. Explain one to the other what a mixture is and the other student to explain what a pure substance is.
3. Agree and write down their explanations.

Open a large packet of Smarties and spread them out on a sheet of white paper. Invite students to describe what they see.

1. Ensure that the word mixture is used and understood.
2. Separate into piles of ‘like’ sweets.
3. Describe how this might be used as a model for the particles of which substances are made.

Share the objectives with the students and explain that they will look at modelling more carefully.

Particle card sorting 1

Give each pair a pack of ’Particle cards’. Ask them to sort the cards into two heaps: mixtures and pure substances.

Plenary

1. When finished, lead a class discussion using the prompt questions:
   • How does this help you ‘picture’ the difference between mixtures and pure substances?
   • How does it fit with the explanation you wrote earlier?
   • What might you want to add to your explanation?
2. Go around the pairs and ask students in turn to hold up a card that represents either a mixture or a pure substance (it must be different to others that have been shown). Ask the remainder of the class if they think each card is correct, and if not why they think differently.
3. Reinforce the same ideas using 3D models. Fill large beakers with different ‘particles’ made from suitable molecular modelling kits. Invite students to identify which are mixtures and which are pure substances, by using ’thumbs up’ or ’traffic light’ cards.
4. Explain the value of using 3D models of particles rather than 2D pictures.

Particle card sorting 2

1. Ask each pair to sort the piles of pure substances cards into further ‘like’ piles.
2. With the whole class, invite pairs to explain the reasons for sorting the cards as they did. This is an opportunity to draw out the ideas of (a) elements and compounds, and (b) solids, liquids and gases.

Commentary

Although working in pairs, students are making an assessment of their own understanding at each stage of this session. Any insecurity about individual learning is not, however, exposed to the whole class as they give their responses jointly.

Teacher questions have an important role in confirming and reinforcing the concepts.

Practical notes

Stimuli

• A large packet of Smarties
• A2 sheet of white paper

Other equipment

• Set of ’traffic light’ cards

Answers

Particle cards

Page	Top picture	Middle picture	Bottom picture
1	liquid; mixture; elements	gas; mixture; elements	solid; mixture; elements
2	gas; pure; element	liquid; pure; element	solid; pure; element
3	liquid; mixture; compound	gas; mixture; compounds	liquid; mixture; compounds
4	gas; pure; element	liquid; pure; element	solid; pure; element
5	gas; pure; element	liquid; pure; element	solid; pure; element
6	gas; pure; element	liquid; pure; element	solid; pure; element
7	gas; pure; element	liquid; pure; element	solid; pure; element
8	gas; mixture; elements	gas; mixture; element and compound	gas; mixture; compounds
9	gas; pure; compound	liquid; pure; compound	solid; pure; compound
10	gas; pure; compound	liquid; pure; compound	solid; pure; compound
11	gas; pure; compound	liquid; pure; compound	solid; pure; compound
12	gas; pure; element	liquid; pure; element	solid; pure; element
13	liquid; mixture; elements	gas; mixture; elements	liquid; mixture; elements
14	gas; pure; element	liquid; pure; element	solid; pure; element