• 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 sheet of paper? (alpha (α) / beta (β) / gamma (γ)) → alpha (α)Prompt: The more ionising the radiation, the less penetrating it is.
2. An atom of potassium is written ³⁹₁₉K (mass number 39, atomic number 19). How many protons does it have? → 19Prompt: Atomic number = number of protons (= electrons in a neutral atom).
3. Why are gamma rays used to sterilise medical equipment in sealed packs? (They pass through the packaging and kill microbes / They heat the equipment to 1000 °C / They are stopped by plastic / They make the equipment radioactive) → They pass through the packaging and kill microbesPrompt: Gamma is very penetrating.

• 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. radium-226 (mass number 226, atomic number 88) undergoes alpha decay to form Rn. What is the atomic number of the new nucleus? → 86Prompt: An alpha particle is ⁴₂He: it takes away 4 from the mass number and 2 from the atomic number.
2. A nucleus with A = 90, Z = 38 decays into a nucleus with A = 90, Z = 39. 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 8 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. In alpha decay, by how much does the mass number decrease? (1 / 0 / 4 / 2) → 4Prompt: An alpha particle has 2 protons and 2 neutrons.
2. carbon-14 (mass number 14, atomic number 6) undergoes beta decay to form N. What is the atomic number of the new nucleus? → 7Prompt: In beta decay a neutron becomes a proton and an electron (⁰₋₁e) is emitted.

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