Gas Particles and Mass

Overview

In this lesson, students use particle models to explain why gases show different observable properties from solids and liquids, focusing on the key idea that gases have mass. Students plan and run a fair micro-investigation, then use evidence to draw a reasoned conclusion.

Learning intentions

WALT:

• explain observable properties of gases using a particle motion and arrangement model
• describe how gases can have mass and how this can be investigated
• plan a repeatable investigation by choosing variables and controlling a fair test
• record measurements precisely and use evidence to support a conclusion

Success criteria

I can:

• model particles in gases (moving freely, spaced apart) and link this to properties I observe
• explain why a gas-filled container can have different mass to an empty one
• identify the independent, dependent, and controlled variables in our investigation plan
• use data to write a reasoned conclusion and note at least one possible source of error

Curriculum links

• AC9S5U04: explain observable properties of solids, liquids and gases by modelling the motion and arrangement of particles
• AC9S5I02: plan and conduct repeatable investigations, including fair testing decisions, risks, and safe equipment use
• AC9S5I03: use equipment to observe, measure and record data with reasonable precision
• AC9S5I05: compare methods/findings, recognise sources of error, pose questions for further investigation, and draw reasoned conclusions

Lesson structure ({total minutes})

1. 0–5 min · Hook (thinking routine: See–Think–Wonder). Teacher shows two quick images or props: an empty balloon and a balloon filled with air, and asks students to complete See–Think–Wonder in notebooks (no sharing yet). Students write: what they see, what they think is happening to particles, and what they wonder about mass.

2. 5–15 min · Direct teach: Particle model of gases (properties focus). Teacher uses a simple role-play or gesture model: particles are far apart and constantly moving; no fixed shape or volume. Students “become particles” briefly and then complete a sentence: “Because gas particles are ___, gases show the property that ___.”

3. 15–25 min · Demonstration: Gases have mass (prediction). Teacher demonstrates (or simulates) comparing an empty balloon with one filled with air on a balance. Teacher pauses before the reading: “What do you predict and why?” Students use a short reasoning frame: Claim–Reason–Evidence (evidence here is the particle model), then record their prediction.

4. 25–35 min · Investigation planning (fair test + repeatable method). Teacher gives a simple task: “Measure mass of a container with and without air.” Students work in groups to write a method that another group could repeat. Teacher prompts for: independent variable (air added yes/no), dependent variable (mass), controlled variables (same container, same balloon/cap, same handling time, same scale, same orientation). Students also list risks (e.g., balloon popping; careful with equipment) and safe handling.

5. 35–48 min · Conduct investigation (collect data with precision). Teacher circulates and checks precision (read at eye level; record units; avoid touching the balance platform). Students run the test at least two trials: measure empty container, then measure after adding air (e.g., inflated balloon attached to container lid, or sealed syringe with air). Students record results in a table: trial number, mass, and observations.

6. 48–55 min · Compare findings + recognise errors (thinking routine: Claim–Check–Revise). Teacher leads a quick class comparison: Which results match the prediction? Which don’t, and why might that be? Students complete Claim–Check–Revise: state a claim, check it against their data, and revise if needed. Teacher explicitly draws attention to possible sources of error (unequal air amount, leaking seal, reading scales incorrectly, container not dry/cool, handling causing mass transfer).

7. 55–60 min · Exit ticket (reasoned conclusion). Students answer: “Using the particle model, explain why the gas has mass. Then write one way your investigation could be improved.” Teacher collects for quick review.

Resources

• Balloons or air-filled syringes and seals (rubber stoppers/clips) for comparison
• Measuring balance (or digital scale), weights/holders as needed
• Containers for air/no-air comparison (same size and material)
• Data recording sheets or science journals with tables
• Safety glasses if required by school policy
• Timer for trial consistency
• Whiteboard/slide prompts for See–Think–Wonder and reasoning frames

Assessment

• Formative: Observe student particle modelling explanations during role-play/gesture task
• Formative: Check investigation planning for correct identification of independent/dependent/controlled variables and safe procedures
• Formative: Review measurement recordings for reasonable precision and correct units
• Exit ticket: Reasoned explanation linking particle model to the idea that gases have mass, plus one improvement or error source

Differentiation

• Support: Provide sentence starters for reasoning (e.g., “I claim that… because… Our evidence shows…”), and a partially completed variables table for planning
• Support: Use a checklist for “fair test” and a number line or example table to help students record consistently
• Extension for advanced learners: Add a quantitative challenge—determine whether “more air” (different inflation levels) changes mass; students propose a new fair test and identify which variable would change and which would be controlled
• EAL/SEN: Offer visual supports (particle diagrams, icon cards for variables) and allow oral responses before writing; group roles can be assigned (measurer, recorder, timekeeper, safety checker)
• Manage equipment variation: Provide extra guidance if some groups experience leaks or inconsistent air amounts; prompt them to troubleshoot seals and repeat trials

Extension (optional)

• Students pose one new investigable question based on today’s evidence (e.g., “Does gas mass change when temperature changes?”) and write a brief method outline for a future test.