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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: no charge and no mass? (alpha (α) / beta (β) / gamma (γ)) → gamma (γ)Prompt: The more ionising the radiation, the less penetrating it is.
  2. An atom of boron is written ¹¹₅B (mass number 11, atomic number 5). How many protons does it have? → 5Prompt: Atomic number = number of protons (= electrons in a neutral atom).
  3. A factory checks the thickness of paper with radiation passing through it. Which type is best? (alpha / beta / gamma / none: radiation cannot pass through paper) → betaPrompt: Alpha would be stopped completely; gamma would hardly change.

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. strontium-90 (mass number 90, atomic number 38) undergoes beta decay to form Y. What is the atomic number of the new nucleus? → 39Prompt: In beta decay a neutron becomes a proton and an electron (⁰₋₁e) is emitted.
  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.

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 = 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. strontium-90 (mass number 90, atomic number 38) undergoes beta decay to form Y. What is the mass number of the new nucleus? → 90Prompt: 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

    In alpha decay, by how much does the mass number decrease?

    • A. 4
    • B. 0
    • C. 2
    • D. 1

  2. Question 2

    A nucleus with A = 14, Z = 6 decays into a nucleus with A = 14, Z = 7. What type of decay is this?

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

  3. Question 3

    cobalt-60 (mass number 60, atomic number 27) undergoes beta decay to form Ni. What is the atomic number of the new nucleus?

    Answer

  4. Question 4

    In beta decay, where does the emitted electron come from?

    • A. the air around the atom
    • B. the outer electron shell
    • C. a neutron in the nucleus changing into a proton
    • D. a proton splitting in two

  5. Question 5

    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

  6. Question 6

    radium-226 (mass number 226, atomic number 88) undergoes alpha decay to form Rn. What is the atomic number of the new nucleus?

    Answer

  7. Question 7

    Why does the element change in alpha and beta decay?

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

  8. Question 8

    A nucleus with A = 241, Z = 95 decays into a nucleus with A = 237, Z = 93. What type of decay is this?

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

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Answer key: Balance alpha and beta decay equations

  1. 1. A. 4

  2. 2. B. beta decay

  3. 3. 28

  4. 4. C. a neutron in the nucleus changing into a proton

  5. 5. B. beta decay

  6. 6. 86

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

  8. 8. A. alpha decay