Help your students develop their understanding of gases, liquids and solids using the particle model in this lesson plan with activities for 11–14 year olds

Students think about gases, liquids and solids in terms of the particle model. They interpret diagrams on cards showing representations of particles and may observe a teacher demonstration.

The activity provides an opportunity for students to:

  • Reinforce their understanding of the terms gas, liquid and solid.
  • Explore the use of models to describe gases, liquids and solids.

Learning objectives

Students will be able to describe that:

  • Substances are made up of tiny particles.
  • The difference between solids, liquids and gases can be explained using the particle model.

Sequence of activities

Introduction and demonstration

  1. Display four to five samples of a solid, four to five samples of a liquid, and four to five samples of a gas (ideally two should be coloured, eg chlorine or bromine).
  2. As an option, use some demonstrations to show change of state (see ‘Examples of change of state’ sheet).
  3. Invite students to describe what they see.
  4. Ensure that the words gas, liquid and solid are used and understood.
  5. Share the objectives with the students and explain that they will look at modelling to describe gases, liquids and solids, and to explain differences in their properties.

Activity 1: Particle cards

Arrange students to work in pairs. Give each pair a full set of ’Particle cards’, and ask them to sort the cards into three heaps:

  • Particles close to one another and neatly ordered.
  • Particles close to one another and randomly organised.
  • Particles not close together and randomly organised.


 In a plenary, invite students to say:

  1. What they think ‘neatly ordered’ and ‘randomly organised’ mean.
  2. Which pile represents solids, which liquids and which gases.

Make sure there is no confusion of particle meaning grain or crystal (eg of sugar or salt) and meaning the tiniest thing of which something is made up (eg atom, molecule, ion).

Activity 2: Gases, liquids and solids

  1. Give each student a copy of the ‘Gases, liquids and solids’ worksheet.
  2. Agree with the students the criteria that will be used to assess their responses and explain how the assessment will be made.
  3. Ask students to work individually to complete the boxes on the sheet. (Mini whiteboards might be used by students to sketch the particle pictures before committing these to paper.)
  4. When students have completed their sheets, ask them to:
    • Assess their partner’s sheet.
    • Act as advocate for their partner’s success.
    • Collect a badge for their partner.


Purpose and criteria for successful outcomes of the work are made explicit so that students are clear about what they are doing.

The activities are designed to help students order their thoughts, with discussion and questions playing a part.

Peer advocacy acts as a further stimulus to encourage learning and understanding.

Practical notes


  • Four to five samples of solids
  • Four to five samples of liquids
  • Four to five samples gases – ideally two should be coloured, eg chlorine (FLAMMABLE and CORROSIVE) or bromine (TOXIC and CORROSIVE depending on concentration)
  • Mini whiteboards, enough for each student
  • Badges, enough for each student

Health, safety and technical notes

  • Read our standard health and safety guidance.
  • It is the responsibility of the teacher to carry out appropriate risk assessments for the demonstrations. There is further information about safety on the demonstration sheet.

Primary teaching notes

If you teach primary science, see the guidance below to find out how to use this resource.

Skill development

Children will develop their working scientifically skills by:

  • Asking their own questions about scientific phenomena.
  • Using appropriate scientific language and ideas to explain, evaluate and communicate their methods and findings.

Learning outcomes

Children will:

  • Compare and group materials together, according to whether they are solids, liquids or gases.

Concepts supported

Children will learn:

  • The differences between solids, liquids and gases in terms of particle distribution.

Suggested activity use

The activity can be used as a model for whole class teaching on the differences between solids, liquids and gases and how they behave.

Some of the ideas may be too complex for primary children to work with alone, but the particle cards could provide a simple way of grouping solids, liquids and gases under the guidance of an adult.

Practical considerations

Sourcing equipment for these activities can be difficult, particularly the equipment for the changes of state optional demonstrations and gas samples.

If terminology is not used correctly, children can develop or reinforce the misconception that atoms, molecules and particles are the same.