OCR · A-Level · Physics
Course version: H556 · Version from Sept 2015
Nuclear fission and fusion: (k) balancing nuclear transformation equations.
Balancing a nuclear transformation equation means making the total nucleon number and the total charge equal on both sides.
Checked against the OCR H556 specification (opens in a new tab) on .
- Point 10 of 18
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Balancing a nuclear transformation equation means making the total nucleon number and the total charge equal on both sides. For example, in ²³⁸U → ²³⁴Th + ⁴He, the left side has 238 nucleons and charge 92, while the right side has 234 + 4 = 238 nucleons and charge 90 + 2 = 92. In beta-minus decay, a neutron changes into a proton and an electron, so the nucleon number stays the same while the charge increases by 1, as in ¹⁴C → ¹⁴N + ⁰e + antineutrino. In beta-plus decay, the charge decreases by 1.
What earns the marks
- The total nucleon number is the same on both sides of a nuclear transformation equation.
- The total charge is the same on both sides of a nuclear transformation equation.
- Alpha emission reduces nucleon number by 4 and charge by 2.
- Beta-minus emission leaves nucleon number unchanged and increases charge by 1.
- Beta-plus emission leaves nucleon number unchanged and decreases charge by 1.
- A missing particle can be found by subtracting the known totals from the totals on the other side.
Common mistakes and how to put them right
Balancing only nucleon number and forgetting charge.
Put it right: Both totals must be conserved.
Treating an electron as having nucleon number 1.
Put it right: An electron has nucleon number 0 and charge 1⁻.
Adding the mass numbers of the products instead of equating them to the reactant.
Put it right: The totals must match on both sides.
Mixing up alpha and beta decay changes.
Put it right: Alpha reduces both nucleon number and charge, while beta-minus changes charge only.
Exam tips
- Write the nucleon and charge totals above each side before choosing an option.
- For a missing nuclide, subtract the known product totals from the reactant totals.
- Check the sign of the charge for beta particles and positrons.
- Use the periodic table or given data to match the proton number to the correct element symbol.
Try the lesson
The start of the Nuclear fission and fusion: (k) balancing nuclear transformation equations. lesson, made from checked teaching notes for this specification point.
Listen
Balancing a nuclear transformation equation means making the total nucleon number and the total charge equal on both sides. For example, in ²³⁸U → ²³⁴Th + ⁴He, the left side has 238 nucleons and charge 92, while the right side has 234 + 4 = 238 nucleons and charge 90 + 2 = 92. In beta-minus decay, a neutron changes into a proton and an electron, so the nucleon number stays the same while the charge increases by 1, as in ¹⁴C → ¹⁴N + ⁰e + antineutrino. In beta-plus decay, the charge decreases by 1. A strong answer earns marks for these points. The total nucleon number is the same on both sides of a nuclear transformation equation. The total charge is the same on both sides of a nuclear transformation equation. Alpha emission reduces nucleon number by 4 and charge by 2. Beta-minus emission leaves nucleon number unchanged and increases charge by 1. Exam tip: Write the nucleon and charge totals above each side before choosing an option.
See it
Key words
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Conservation of nucleon number
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Conservation of charge
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Alpha and beta decay
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Nuclear equations and nuclide notation
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See every definition
- Conservation of nucleon number
- The total nucleon number is the same on both sides of a nuclear transformation equation.
- Conservation of charge
- The total charge is the same on both sides of a nuclear transformation equation.
- Alpha and beta decay
- Alpha emission reduces nucleon number by 4 and charge by 2, beta-minus leaves nucleon number unchanged and increases charge by 1, and beta-plus leaves nucleon number unchanged and decreases charge by 1.
- Nuclear equations and nuclide notation
- A missing particle can be found by subtracting the known totals from the totals on the other side, remembering that electrons have nucleon number 0 and charge 1⁻.
Label the diagram
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1Box 1
2Box 2
3Box 3
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