20 Particle models: gas, liquid, solid 11-14 Working in groupsSelf assessmentPeer assessmentSharing objectives and criteriaQuestioningUsing feedbackUsing tests

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

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).

As an option, use some demonstrations to show change of state.

Invite students to describe what they see.

Ensure that the words gas, liquid and solid are used and understood.

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.

Arrange students to work in pairs. Give each pair a full set of Particle cards.

Ask each pair 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:

  • what they think ‘neatly ordered’ and ‘randomly organised’ mean
  • 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).

Give each student a copy of the Gases, liquids and solids worksheet.

Agree with the students the criteria that will be used to assess their responses and explain how the assessment will be made.

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.

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.

Assessment for learning commentary

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.



  • 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)

Optional demonstration

Download Word Download PDF Examples of change of state


For each pair of students

Download Word Download PDF Set of Particle cards

For each student

Download Word Download PDF Gases, liquids and solids
  • Mini whiteboard
  • Badge.

Safety note

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.