OCR · GCSE · Physics
Course version: J249 · Version from Sept 2018
Use names and symbols of common nuclei and particles to write balanced…
Full specification wording
Radioactive emissions: use names and symbols of common nuclei and particles to write balanced equations that represent radioactive decay
A nuclear equation is balanced when the mass numbers and the proton numbers each add up to the same total on both sides.
Checked against the OCR J249 specification (opens in a new tab) on .
- Point 6 of 12
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A nuclear equation is balanced when the mass numbers and the proton numbers each add up to the same total on both sides. Write the parent nucleus with its mass number as a superscript and its proton number as a subscript, for example uranium-238 as ²³⁸₉₂U. Then write the emitted particle with its own numbers: an alpha particle as ⁴₂He, a beta particle as ⁰₋₁e, and a gamma photon as ⁰₀γ. The daughter nucleus is found by subtraction. For alpha decay of ²³⁸₉₂U, the daughter has mass number 238 − 4 = 234 and proton number 92 − 2 = 90, giving ²³⁴₉₀Th. For beta decay the mass number is unchanged and the proton number rises by 1. Check the totals on each side match before accepting an equation. Use element symbols correctly and keep the superscript and subscript in their proper positions.
What earns the marks
- Writes the parent nucleus with its mass number as a superscript and proton number as a subscript.
- Uses the correct symbol and numbers for the emitted particle, such as ⁴₂He for alpha or ⁰₋₁e for beta.
- Balances the equation so the total mass number is equal on both sides.
- Balances the equation so the total proton number is equal on both sides.
- Finds the daughter nucleus by subtracting the emitted particle's numbers from the parent's.
Common mistakes and how to put them right
Writes the mass number and proton number the wrong way round.
Put it right by placing the mass number as the superscript and the proton number as the subscript.
Balances only the mass number and ignores the proton number.
Put it right by checking both totals on each side.
Gives the beta particle a mass number of 1.
Put it right by writing it as ⁰₋₁e with mass number 0.
Forgets to change the element symbol when the proton number changes.
Put it right by choosing the symbol that matches the new proton number.
Exam tips
- Write the mass and proton numbers above and below each symbol before balancing.
- Subtract the emitted particle's numbers from the parent to find the daughter's numbers.
- Check both totals on each side of the arrow before selecting an answer.
- Remember that a beta particle has proton number −1, so the daughter's proton number rises by 1.
Try the lesson
The start of the Radioactive emissions: use names and symbols of common nuclei and particles to write balanced equations that represent radioactive decay lesson, made from checked teaching notes for this specification point.
Have a go first
In a nuclear decay equation, which symbol represents a beta particle?
Listen
A nuclear equation is balanced when the mass numbers and the proton numbers each add up to the same total on both sides. Write the parent nucleus with its mass number as a superscript and its proton number as a subscript, for example uranium-238 as ²³⁸₉₂U. Then write the emitted particle with its own numbers: an alpha particle as ⁴₂He, a beta particle as ⁰₋₁e, and a gamma photon as ⁰₀γ. The daughter nucleus is found by subtraction. For alpha decay of ²³⁸₉₂U, the daughter has mass number 238 − 4 = 234 and proton number 92 − 2 = 90, giving ²³⁴₉₀Th. For beta decay the mass number is unchanged and the proton number rises by 1. Check the totals on each side match before accepting an equation. Use element symbols correctly and keep the superscript and subscript in their proper positions. A strong answer earns marks for these points. Writes the parent nucleus with its mass number as a superscript and proton number as a subscript. Uses the correct symbol and numbers for the emitted particle, such as ⁴₂He for alpha or ⁰₋₁e for beta. Balances the equation so the total mass number is equal on both sides. Balances the equation so the total proton number is equal on both sides. A common slip: Writes the mass number and proton number the wrong way round. Instead, placing the mass number as the superscript and the proton number as the subscript. Exam tip: Write the mass and proton numbers above and below each symbol before balancing.
Key words
Say what each word means before you turn the card.
Nuclear notation with mass and proton numbers
Try answering aloud or in your head before turning the card.
Symbols for alpha, beta and gamma emissions
Try answering aloud or in your head before turning the card.
Balancing mass numbers in decay equations
Try answering aloud or in your head before turning the card.
See every definition
- Nuclear notation with mass and proton numbers
- Writing a nucleus with its mass number as a superscript and its proton number as a subscript, for example uranium-238 as ²³⁸₉₂U.
- Symbols for alpha, beta and gamma emissions
- The emitted particles written with their own numbers: an alpha particle as ⁴₂He, a beta particle as ⁰₋₁e, and a gamma photon as ⁰₀γ.
- Balancing mass numbers in decay equations
- A nuclear equation is balanced when the mass numbers add up to the same total on both sides.
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