• Quick retrieval from earlier learning (Alpha, beta and gamma radiation; Atomic number, mass number and isotopes). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Which type of radiation: a fast-moving electron from the nucleus? (alpha (α) / beta (β) / gamma (γ)) → beta (β)Prompt: The more ionising the radiation, the less penetrating it is.
2. An atom of helium is written ⁴₂He (mass number 4, atomic number 2). How many protons does it have? → 2Prompt: Atomic number = number of protons (= electrons in a neutral atom).
3. Smoke detectors contain a source that emits alpha particles. Why alpha? (Alpha has the longest range / Alpha passes through walls / Alpha is an electromagnetic wave / Alpha ionises the air strongly but is stopped by smoke and cannot leave the detector) → Alpha ionises the air strongly but is stopped by smoke and cannot leave the detectorPrompt: Smoke blocks the particles, changing the current.

• Show the periodic table and ask what patterns students can see before anything is explained.
• Share the objective: Balance alpha and beta decay equations. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: strontium-90 (mass number 90, atomic number 38) undergoes beta decay to form Y. What is the atomic number of the new nucleus?
• Step 1: A: 90 (unchanged); Z: 38 + 1 = 39
• Step 2: So the answer is: 39
• Answer: 39
• Pause after each step and ask a student to say what comes next.

• Do these together. Students try each step on whiteboards before you reveal it.
• Use the hints as prompts rather than giving the answer.

1. iodine-131 (mass number 131, atomic number 53) undergoes beta decay to form Xe. What is the mass number of the new nucleus? → 131Prompt: In beta decay a neutron becomes a proton and an electron (⁰₋₁e) is emitted.
2. A nucleus with A = 226, Z = 88 decays into a nucleus with A = 222, Z = 86. What type of decay is this? (alpha decay / beta decay / gamma emission only) → alpha decayPrompt: Look at how the mass number changes.

• Students work on the student sheet. Circulate and check the first two answers of every student early.
• Students who finish: write a question of their own for a partner, with the answer.

The 6 questions are on the student sheet below, with answers in the key.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. polonium-210 (mass number 210, atomic number 84) undergoes alpha decay to form Pb. What is the atomic number of the new nucleus? → 82Prompt: An alpha particle is ⁴₂He: it takes away 4 from the mass number and 2 from the atomic number.
2. A nucleus with A = 238, Z = 92 decays into a nucleus with A = 234, Z = 90. What type of decay is this? (alpha decay / beta decay / gamma emission only) → alpha decayPrompt: Look at how the mass number changes.

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-11.