Teaching sequence

Lesson objective

Students develop an understanding of the observable properties and behaviours of gases.


Revisit students’ current understanding about the properties and behaviours of a gas by reviewing the list and statements constructed by the students in lesson 1.

Ask the class to consider the following questions.

  • Can a gas be observed using any of your senses? For example, can you see it? Can you smell it?
  • Does a gas have a definite shape?
  • Does a gas have mass?
  • Does a gas have volume?
  • Does it take up space?

Allow discussion time around these questions. Ask students for evidence to support their responses.

View the video CO2 is heavier than air. Ask the students to discuss what they saw in the video and what it told them about the properties of a gas.

Explain to the students that they are going to do some mini-investigations that will help them understand the properties of a gas.

Teacher note: More information on these mini-investigations can be found in Background information (PDF, 494 KB).


  1. Half fill a large, clear container with water. Invert a drinking glass and push it into the water, trapping air inside the glass. Ask the students to make predictions about what will happen if the glass inside the container is tipped slightly. Have students explain the reasons for their predictions. Tip the glass slightly to allow a bubble of air to escape. Ask the students to consider what this helps prove about the properties of a gas.
  2. Organise students into cooperative learning teams and provide each team with a copy of the worksheet Investigating a gas (Word, 386 KB) and the necessary equipment. Allow them time to investigate Challenge 1 on the worksheet.
  3. Meet together as a class to share the students’ results and discuss how this helps demonstrate that a gas takes up space.
  4. Present each team with an inflated and a deflated balloon and ask them to consider how these balloons are evidence of the fact that a gas takes up space. Ask the students what the inflated balloon would look like if a gas did not take up space. What happens to the air in a balloon when it is released? Where does it go? What space does it take up then?
  5. Allow students time to read and complete challenge 2 on the worksheet. Meet together as a class to share results and discuss how this helps demonstrate that a gas has mass.


Revisit the questions discussed in the introduction of this lesson. Discuss what evidence the students have from their investigations that might assist them in answering these questions. Can they think of any other examples that show the properties of gas?

Ask students to record their responses to at least two of the questions in an appropriate place such as their science book.

Lesson Resources


Student activities

Digital resources

CO2 is heavier than air YouTube (1.11 min) Video 


Investigating a gas, (Word, 386 KB)

Useful links

A gas is matter,
Department of Education and Early Childhood Development, Victoria. Teaching resource 

Looking for a gas,
Chem4Kids. Information for students 

Very simple demonstration that shows air takes up space,
YouTube (1:14 min). Video