AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
In a nuclear equation an alpha particle may be represented by the symbol:…
Full specification wording
Nuclear equations: In a nuclear equation an alpha particle may be represented by the symbol: and a beta particle by the symbol: The emission of the different types of nuclear radiation may cause a change in the mass and /or the charge of the nucleus. For example: So alpha decay causes both the mass and charge of the nucleus to decrease.
In an equation the alpha particle is written ⁴₂He, because it is two protons and two neutrons, and the beta particle is written ⁰₋₁e, because it is an electron with negligible mass and a charge of -1.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 2 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
In an equation the alpha particle is written ⁴₂He, because it is two protons and two neutrons, and the beta particle is written ⁰₋₁e, because it is an electron with negligible mass and a charge of -1. In alpha decay the nucleus loses two protons and two neutrons, so its mass number falls by 4 and its atomic number falls by 2: ²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He. Both numbers decrease, which is what distinguishes alpha decay at a glance. Because the atomic number has changed, the daughter is a different element, sitting two places earlier in the periodic table. Check the equation by adding each column: 234 + 4 = 238 and 90 + 2 = 92.
What earns the marks
- Representing the alpha particle as ⁴₂He and the beta particle as ⁰₋₁e.
- Reducing the mass number of the nucleus by 4 in alpha decay.
- Reducing the atomic number of the nucleus by 2 in alpha decay.
- A completed equation in which both the mass numbers and the atomic numbers balance.
Common mistakes and how to put them right
Writing ⁴₂He correctly but forgetting to subtract 4 and 2 from the original nucleus.
Taking 2 off the mass number and 4 off the atomic number.
Giving the beta particle a mass number of 1 instead of 0.
Writing the charge on the beta particle as +1 rather than -1.
Exam tips
- Memorise the two symbols exactly; a wrong subscript loses the balancing marks that follow.
- Subtract 4 and 2 as a single habit for alpha, then check the columns add up.
- Alpha decay is the only common decay in which both numbers fall, which makes it easy to spot.
Try the lesson
The start of the Nuclear equations: In a nuclear equation an alpha particle may be represented by the symbol: and a beta particle by the symbol: The emission of the different types of nuclear radiation may cause a change in the mass and /or the charge of the nucleus. For example: So alpha decay causes both the mass and charge of the nucleus to decrease. lesson, made from checked teaching notes for this specification point.
Have a go first
Which symbol represents an alpha particle in a nuclear equation?
Listen
In an equation the alpha particle is written ⁴₂He, because it is two protons and two neutrons, and the beta particle is written ⁰₋₁e, because it is an electron with negligible mass and a charge of -1. In alpha decay the nucleus loses two protons and two neutrons, so its mass number falls by 4 and its atomic number falls by 2: ²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He. Both numbers decrease, which is what distinguishes alpha decay at a glance. Because the atomic number has changed, the daughter is a different element, sitting two places earlier in the periodic table. Check the equation by adding each column: 234 + 4 = 238 and 90 + 2 = 92. A strong answer earns marks for these points. representing the alpha particle as ⁴₂He and the beta particle as ⁰₋₁e. reducing the mass number of the nucleus by 4 in alpha decay. reducing the atomic number of the nucleus by 2 in alpha decay. a completed equation in which both the mass numbers and the atomic numbers balance. Exam tip: Memorise the two symbols exactly; a wrong subscript loses the balancing marks that follow.
See it
Key words
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alpha decay
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symbols for emitted particles
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changes in mass number
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changes in atomic number
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See every definition
- alpha decay
- A type of decay that causes both the mass and charge of the nucleus to decrease.
- symbols for emitted particles
- An alpha particle may be represented by one symbol and a beta particle by another in a nuclear equation.
- changes in mass number
- Alpha decay reduces the mass number of the nucleus by 4.
- changes in atomic number
- Alpha decay reduces the atomic number of the nucleus by 2.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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Test your understanding of Nuclear equations: In a nuclear equation an alpha particle may be represented by the symbol: and a beta particle by the symbol: The emission of the different types of nuclear radiation may cause a change in the mass and /or the charge of the nucleus. For example: So alpha decay causes both the mass and charge of the nucleus to decrease.
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