States of Matter Intro

Overview

In today’s lesson students model how particles are arranged and how they move in solids, liquids and gases to explain observable properties. They will also investigate gases by catching air in a soft plastic bag and use a role-play model to deepen understanding.

Learning intentions

• Students will model solids, liquids and gases using particle arrangement and motion.
• Students will explain observable properties of gases using evidence from a simple investigation.
• Students will plan and follow a safe, repeatable investigation to explore a gas (air).
• Students will communicate findings using scientific language and a thinking routine.

Success criteria

• I can describe how gas particles are arranged and how they move compared with solids and liquids.
• I can observe and record what happens when we catch air in a plastic bag.
• I can use evidence to explain why gases spread out and can be compressed.
• I can compare my results with others and suggest possible reasons for differences.

Curriculum links

• AC9S5U04 — explain observable properties of solids, liquids and gases by modelling particle motion and arrangement.
• AC9S5I02 — plan and conduct a repeatable investigation, including deciding variables, risks and safe use of equipment.
• AC9S5I03 — use equipment to observe, measure and record data with reasonable precision.
• AC9S5I05 — compare methods/findings with others, recognise sources of error, and draw reasoned conclusions.
• AC9S5I06 — write/create a short text or explanation to communicate ideas and findings for an audience.

Lesson structure (60 minutes)

1. 0–5 min · Introduction to Matter and States.

• Define Matter: anything that has mass (weight) and takes up space (volume).
• Explain that matter exists in three states: solids, liquids, and gases.
• Describe properties:
  • Solids have definite shape and volume.
  • Liquids have definite volume but indefinite shape.
  • Gases have indefinite shape and indefinite volume.
• Highlight that solids and liquids can be seen and touched, with visible shapes or boundaries.
• Emphasize that gases are invisible but still occupy space (have volume).

2. 5–15 min · Video viewing (YouTube stop-and-think). Teacher plays the YouTube video, pausing at key moments to prompt observations and particle ideas. Students complete a two-column note: “Observed” vs “Particle idea”.

3. 15–25 min · Gas investigation: Catch air. Teacher demonstrates safety and procedure for catching air in a soft plastic bag. Students work in groups to:

• Collect air by holding the bag open and moving through still air.
• Observe and record bag shape, size, and pressure changes.
• Compare "more air" vs "less air" by repeating carefully.
• Release air and observe spreading.

4. 25–35 min · Direct teach: Particle models. If time allows. Teacher explains particle arrangement and motion for solids, liquids, and gases. Students update a class particle chart with arrows and labels.

5. 35–45 min · Particle role-play (Model the evidence). Teacher sets up zones for solids, liquids, gases. Students role-play particle behavior:

• Solid: close together, vibrating.
• Liquid: close but sliding past.
• Gas: spaced out, moving freely. Teacher links role-play to observations from air-catching activity.

6. 45–55 min · Thinking routine: Claim–Evidence–Reasoning (CER). Teacher models CER using gas behavior and bag observations. Students complete CER and share with partners.

7. 55–60 min · Whole-class share and exit check. Teacher highlights key scientific language. Students complete exit ticket: “One property of gases is ___ because particles are ___ and move ___.”

Resources

• Soft plastic bags (enough for 6–8 groups)
• Observation recording sheet/table (group or individual)
• Mini whiteboards or scrap paper for hook/exit ticket
• Timer
• Room markers for solid/liquid/gas zones (cones or paper labels)
• Safety reminders poster (no running with bags, keep bags away from faces)
• Optional digital device for video access and screen projection
• Sentence starters for CER (e.g., “My claim is…”, “Evidence shows…”, “This is because…”)

Assessment

• Formative during video stops: students’ “Observed vs Particle idea” notes
• Check investigation records: do students include measurable/clear observations (e.g., bag size/shape change)?
• CER quality: identifies evidence and connects it to particle arrangement and motion
• Exit ticket: assesses correct particle-based explanation of gas properties

Differentiation

• Support:
• Provide sentence starters and a word bank (gas, particles, spread, move freely, compress) for CER.
• Use a partially completed particle chart with prompts (arranged close/far; fixed/sliding/free).
• Offer a role-play script card so students know what to do in each zone.
• Scaffold investigation repeatability:
• Give groups a simple checklist and a consistent method reminder (“open bag wide, capture in same way, record the same observations each trial”).
• Reduce variables: focus on “more vs less air” only, and keep capture method similar.
• Extension (advanced learners):
• Add a compression challenge: compare results when the same bag is gently pressed versus not pressed, and propose how that links to particle spacing.
• Ask for a fair-test refinement: “What would you measure to make this investigation more precise, and what would you keep the same?”
• EAL/SEN:
• Use visual cues (zones, arrows on the particle chart) and allow oral responses before writing.
• Pair learners strategically so all students can participate in role-play and recording.

Extension

• Advanced option for early finishers: design a second test question (e.g., “How does bag size change when more air is trapped?”) and write a brief method with variables and a risk note, then share with the class.