• 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: stopped by a few mm of aluminium? (alpha (α) / beta (β) / gamma (γ)) → beta (β)Prompt: The more ionising the radiation, the less penetrating it is.
2. An atom of nitrogen is written ¹⁴₇N (mass number 14, atomic number 7). How many electrons does it have? → 7Prompt: Atomic number = number of protons (= electrons in a neutral atom).
3. Smoke detectors contain a source that emits alpha particles. Why alpha? (Alpha is an electromagnetic wave / Alpha has the longest range / Alpha ionises the air strongly but is stopped by smoke and cannot leave the detector / Alpha passes through walls) → 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. carbon-14 (mass number 14, atomic number 6) undergoes beta decay to form N. What is the mass number of the new nucleus? → 14Prompt: In beta decay a neutron becomes a proton and an electron (⁰₋₁e) is emitted.
2. A nucleus with A = 131, Z = 53 decays into a nucleus with A = 131, Z = 54. What type of decay is this? (alpha decay / beta decay / gamma emission only) → beta 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. A nucleus with A = 60, Z = 27 decays into a nucleus with A = 60, Z = 28. What type of decay is this? (alpha decay / beta decay / gamma emission only) → beta decayPrompt: Look at how the mass number changes.
2. In beta decay, where does the emitted electron come from? (a neutron in the nucleus changing into a proton / the outer electron shell / a proton splitting in two / the air around the atom) → a neutron in the nucleus changing into a protonPrompt: The atomic number goes up by one.

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