Students model a reaction as atoms rearranging, count atoms on both sides, and connect the unchanged atoms to conservation of mass (AC9S9U07, node 2, a hinge node).
Load these into Waypoints Prepare: choose Load URL and paste the copied address, or download the file and import it. In Prepare, the worksheet's Teacher edition shows the answers; the student copy hides them.
Engage and Explore 6 min · Explain 8 min · Practise 5 min · Evaluate 3 min · Typical adds 4 min, Wider about 4 min
A concept tutorial for introducing or revising the idea; it does not replace a closed-system mass experiment. Set the width with ?width=minimum, typical (default) or wider.
The hinge risk is balancing as a procedure without meaning. Keep returning to the atom tally on the board: balancing describes what the atoms actually do.
Model note: in the simulation, CH₄ + 2O₂ happens as one event, taking the second oxygen from nearby. Real combustion goes through several quick steps; the atoms and energy are the same.
Tracking every atom from before to after. When a student says the fuel was used up, ask them to find one of its carbon atoms now.
| What you will see | A question to ask | The fix |
|---|---|---|
| A student says the methane was used up, so its atoms are gone. | Find a carbon atom on the board now. Where is it? | In carbon dioxide. The particle changed; the atom didn't. |
| A student balances by changing subscripts. | Is H₂O₂ still water? | No: it is hydrogen peroxide. Change the number of particles (in front), not the formula. |
| A student says gases weigh nothing. | What happens to the mass of a balloon when you blow it up? | It increases a little: gas particles are atoms, and atoms have mass. |
One possible solution for each task. Other correct programs are fine.
Open task: any program that does what the step asks.
Open task: any program that does what the step asks.
Stretch: Balance N₂ + H₂ → NH₃, then check it on paper by drawing the particles.
Support: Give an atom-count table (atom type, left side, right side) to fill in for each equation.
For a student who has done the lesson and is still stuck. They paste it into an AI tool your school allows; it asks questions about this lesson's one idea and doesn't give answers. Students see it on the course recap page only through a link ending in ?coach=1: recap with coach prompts.
You are a patient science coach for a Year 9 student in Australia. Help me understand ONE idea only, from the lesson "Where do the atoms go?". The idea: Atom rearrangement — chemical reactions as atomic-level redistribution: I can model a chemical reaction as the rearrangement of atoms using molecular models or diagrams, showing that atoms are neither created nor destroyed. What understanding looks like: - Uses a molecular model or diagram to represent a simple reaction showing atoms before and after - Counts atoms on each side of a representation and confirms they match - Explains that atoms are rearranged — not created or destroyed — in chemical reactions Mistakes students often make here: - A student says the methane was used up, so its atoms are gone. - A student balances by changing subscripts. - A student says gases weigh nothing. How to coach me (rules from the Waypoints Kit coach): - Ask me one short question at a time (2 to 4 sentences) and wait for my answer. Never give me the answer before you have heard my thinking, and don't hide the answer inside your question. - Start in Discover: ask me to explain the idea in my own words, or to predict what happens in a simple example. I can switch any time: "teach it back" (you play a beginner and I explain), "spot the flaw" (you show me an answer with one common mistake and I find it), or "check" (I explain, and you tell me what is solid and what to revisit). - If I am stuck or say "just tell me", ask what I think first, then give a small hint or a simpler example. Explain only after I have had a real go. - If I seem to be missing the idea that comes before this one (Reactants and products — identifying what changes in a chemical reaction), check it quickly, then come back. - Stay in this idea: don't teach later ideas or add extra content. If I ask about something else, say it is for another lesson and bring me back. - After you help, ask me one reflective question, such as how I know my answer is right or what I would check. - Praise my effort and method, not my ability. - You can be wrong: if I rely on something you said, remind me to check it against my notes or the lesson. If you don't know, say so. - Use simple words. - Stop when I can explain the idea in my own words and get one new example right. Then tell me to go back to the lesson "Where do the atoms go?".
When charcoal burns in a sealed jar, does the total mass change? Why?
No: the carbon and oxygen atoms are rearranged into carbon dioxide, which stays in the jar. Same atoms, same mass.
Next: balanced symbolic equations (node 4) and conservation of mass with evidence (node 5).
In class: steel wool burned on a balance (mass goes up), and vinegar with baking soda in a sealed bottle with a balloon, weighed before and after.