AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
The emission of the different types of nuclear radiation may cause a…
Full specification wording
Nuclear equations: 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:
When a nucleus emits nuclear radiation, its mass number and atomic number can change.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 4 of 8
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
When a nucleus emits nuclear radiation, its mass number and atomic number can change. Alpha emission removes two protons and two neutrons, so the mass number decreases by 4 and the atomic number decreases by 2: for example, ²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He. Beta emission converts a neutron into a proton and emits an electron, so the mass number stays the same but the atomic number increases by 1: for example, ¹⁴₆C → ¹⁴₇N + ⁰₋₁β. Gamma emission releases energy without changing either the mass number or the atomic number. Nuclear equations must balance in both mass number and atomic number, so the emitted particle's symbol explains exactly how the nucleus changes.
What earns the marks
- Alpha emission decreases the mass number by 4 and the atomic number by 2 because an alpha particle contains two protons and two neutrons.
- Beta emission leaves the mass number unchanged but increases the atomic number by 1 because a neutron changes into a proton and an electron.
- Gamma emission does not change the mass number or the atomic number because it is electromagnetic radiation carrying energy only.
- In every nuclear equation, the total mass number before the change equals the total mass number after, and the total atomic number before equals the total after.
- For example, in ²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He, the mass numbers give 238 = 234 + 4 and the atomic numbers give 92 = 90 + 2.
Common mistakes and how to put them right
Thinking that beta emission changes the mass number.
Put it right: The mass number stays the same because a neutron is replaced by a proton and the emitted electron has negligible mass.
Forgetting to change the atomic number after alpha emission.
Put it right: Subtract 2 from the atomic number because two protons are lost.
Treating gamma emission as if it changes the nucleus.
Put it right: Leave both unchanged because gamma radiation carries away energy only.
Exam tips
- Use a two-row table for mass numbers and atomic numbers when balancing nuclear equations, and check each row separately.
- Link the type of radiation to the change: alpha changes mass by 4 and charge by 2, beta changes charge by 1 only, gamma changes neither.
- After balancing, identify the new element by using the atomic number and the periodic table, and check that the symbol matches the proton number.
Try the lesson
The start of the Nuclear equations: 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: lesson, made from checked teaching notes for this specification point.
Have a go first
An alpha particle is emitted from a nucleus. What happens to the mass number of the nucleus?
Listen
When a nucleus emits nuclear radiation, its mass number and atomic number can change. Alpha emission removes two protons and two neutrons, so the mass number decreases by 4 and the atomic number decreases by 2: for example, ²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He. Beta emission converts a neutron into a proton and emits an electron, so the mass number stays the same but the atomic number increases by 1: for example, ¹⁴₆C → ¹⁴₇N + ⁰₋₁β. Gamma emission releases energy without changing either the mass number or the atomic number. Nuclear equations must balance in both mass number and atomic number, so the emitted particle's symbol explains exactly how the nucleus changes. A strong answer earns marks for these points. Alpha emission decreases the mass number by 4 and the atomic number by 2 because an alpha particle contains two protons and two neutrons. Beta emission leaves the mass number unchanged but increases the atomic number by 1 because a neutron changes into a proton and an electron. Gamma emission does not change the mass number or the atomic number because it is electromagnetic radiation carrying energy only. In every nuclear equation, the total mass number before the change equals the total mass number after, and the total atomic number before equals the total after. A common slip: Thinking that beta emission changes the mass number: the error is assuming a particle is lost from the nucleus. Instead, the mass number stays the same because a neutron is replaced by a proton and the emitted electron has negligible mass. Exam tip: Use a two-row table for mass numbers and atomic numbers when balancing nuclear equations, and check each row separately.
See it
Key words
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Alpha emission
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Beta emission
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Gamma emission
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Nuclear equations
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See every definition
- Alpha emission
- Removes two protons and two neutrons, so the mass number decreases by 4 and the atomic number decreases by 2.
- Beta emission
- Converts a neutron into a proton and emits an electron, so the mass number stays the same but the atomic number increases by 1.
- Gamma emission
- Releases energy without changing either the mass number or the atomic number, because it is electromagnetic radiation carrying energy only.
- Nuclear equations
- Must balance in both mass number and atomic number, so the emitted particle's symbol explains exactly how the nucleus changes.
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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