Students trace a decay sequence, track atomic and mass numbers at each step, and explain how the sequence ends at a stable nucleus (AC9S9U06, node 5, an integration 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 8 min · Explain 10 min · Evaluate 3 min · Typical adds 1 min, Wider about 1 min
A short integration tutorial that follows the half-life lesson. Set the width with ?width=minimum, typical (default) or wider.
The decay board stops at a stable isotope and says whether each step is how the isotope really decays, so students can't wander into impossible chains. The uranium-238 chain used here is the main series: eight alpha and six beta decays, with a few side branches in the full chart that are left out.
Board notes: the board counts alpha (x) and beta (y) decays. Half-lives vary from a fraction of a second to billions of years and aren't shown here.
Keeping two numbers in step. When a student changes only one of the atomic or mass numbers, ask what each particle carried away.
| What you will see | A question to ask | The fix |
|---|---|---|
| A student subtracts 4 from the atomic number for alpha. | How many protons does an alpha particle carry? | Two, so the atomic number falls by 2; the mass number falls by 4. |
| A student changes the mass number in beta decay. | What changes in the nucleus in beta decay? | A neutron becomes a proton: the atomic number rises by 1 and the mass number stays the same. |
Stretch: Thorium-232 decays by 6 alpha and 4 beta decays to a stable lead isotope. Which isotope? (232 − 24 = 208; 90 − 12 + 4 = 82: lead-208.)
Support: Give a two-column table (Alpha, Beta) with the change to atomic and mass number filled in, and ask students to tick the right column at each step on the board.
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 "From uranium to lead". The idea: Decay sequences — how unstable isotopes reach stability: I can describe how a series of decay events transforms an unstable isotope into a stable one, and explain the relationship between the descriptor's descriptor claim that 'natural radioactive decay results in stable atoms'. What understanding looks like: - Traces a named decay sequence and identifies the stable end product - Tracks changes to atomic number and mass number at each decay step - Explains how the sequence of decay events moves the nucleus toward stability Mistakes students often make here: - A student subtracts 4 from the atomic number for alpha. - A student changes the mass number in beta decay. 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 (Half-life — rate of radioactive decay), 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 "From uranium to lead".
Radium-226 (atomic number 88) decays by alpha emission. What are the new atomic and mass numbers?
Atomic number 86, mass number 222: radon-222.
Next: word equations and balancing equations.
In class: draw the decay series on a large wall chart with a bar for each isotope's half-life; ask students to colour the alpha and beta steps.