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Science lesson plan · 11th grade (Year 12 in England) · 45 minutes

Balance alpha and beta decay equations

Atoms, elements and the periodic table

CCSS NGSS.HS-PS1-8England: GCSE Combined Science: Atomic structure (radioactivity) (nuclear equations)

Objective and success criteria

Students will: Balance alpha and beta decay equations.

  • I can answer questions on today's skill on my own, without help.
  • I can explain each step and say why it works.
  • I can check my answer and spot a mistake.

Before and after

Needs first: Alpha, beta and gamma radiation; Atomic number, mass number and isotopes

Leads to: the next skill in this area.

Materials: Periodic tables, Atom model kits, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).

Warm-up · 5 min

  • 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 hydrogen is written ¹₁H (mass number 1, atomic number 1). How many neutrons does it have? → 0Prompt: Atomic number = number of protons (= electrons in a neutral atom).
  3. Why are gamma rays used to sterilise medical equipment in sealed packs? (They are stopped by plastic / They make the equipment radioactive / They heat the equipment to 1000 °C / They pass through the packaging and kill microbes) → They pass through the packaging and kill microbesPrompt: Gamma is very penetrating.

Hook · 5 min

  • 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.

I do: model it · 10 min

  • 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.

We do: guided practice · 10 min

  • 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 atomic number of the new nucleus? → 54Prompt: 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.

You do: independent practice · 10 min

  • 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.

Exit ticket · 5 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. A nucleus with A = 241, Z = 95 decays into a nucleus with A = 237, Z = 93. What type of decay is this? (alpha decay / beta decay / gamma emission only) → alpha decayPrompt: Look at how the mass number changes.
  2. 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.

Watch out for

  • Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
  • Remembering facts without the reason: ask "why?" and "what is the evidence?"

Support and stretch

Support

  • Review first: Alpha, beta and gamma radiation.
  • Use concrete materials: periodic tables.
  • Give the first step of each question, or a partly worked example to finish.
  • Pair with a confident partner for the guided practice.

Stretch

  • Explain a common mistake in writing and how to fix it.
  • Write a word problem that uses today's skill, then solve a partner's.

Homework and more practice

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

Free lesson plan from eurekami.com/lesson-plan-builder

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Balance alpha and beta decay equations

Name

Date

Score/ 8

  1. Question 1

    A nucleus with A = 131, Z = 53 decays into a nucleus with A = 131, Z = 54. What type of decay is this?

    • A. alpha decay
    • B. beta decay
    • C. gamma emission only

  2. Question 2

    uranium-238 (mass number 238, atomic number 92) undergoes alpha decay to form Th. What is the atomic number of the new nucleus?

    Answer

  3. Question 3

    Why does the element change in alpha and beta decay?

    • A. The number of electrons in shells changes
    • B. The number of protons in the nucleus changes
    • C. The mass stays the same
    • D. The atom gets hotter

  4. Question 4

    A nucleus with A = 90, Z = 38 decays into a nucleus with A = 90, Z = 39. What type of decay is this?

    • A. alpha decay
    • B. beta decay
    • C. gamma emission only

  5. Question 5

    carbon-14 (mass number 14, atomic number 6) undergoes beta decay to form N. What is the atomic number of the new nucleus?

    Answer

  6. Question 6

    What happens to a nucleus when it emits gamma radiation?

    • A. It becomes a different element
    • B. Its mass number falls by 4
    • C. Its atomic number goes up by 1
    • D. It loses energy but its mass and atomic numbers stay the same

  7. Question 7

    A nucleus with A = 210, Z = 84 decays into a nucleus with A = 206, Z = 82. What type of decay is this?

    • A. alpha decay
    • B. beta decay
    • C. gamma emission only

  8. Question 8

    iodine-131 (mass number 131, atomic number 53) undergoes beta decay to form Xe. What is the mass number of the new nucleus?

    Answer

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Answer key: Balance alpha and beta decay equations

  1. 1. B. beta decay

  2. 2. 90

  3. 3. B. The number of protons in the nucleus changes

  4. 4. B. beta decay

  5. 5. 7

  6. 6. D. It loses energy but its mass and atomic numbers stay the same

  7. 7. A. alpha decay

  8. 8. 131