Explain element changes in alpha and beta-minus decay
Use changing nuclear proton number to identify when radioactive decay changes an element.
Section P5.2.3 · Radioactive decay
Cross-referenced from the related Cambridge IGCSE Chemistry 0620 or Physics 0625 teaching to the 0652 syllabus. Exact 0652 Core/Supplement objective coverage and this final-series course’s examiner fit still need specialist review. Written practice is self-checked and does not predict a Cambridge grade or demonstrate supervised laboratory competence.
Before you begin
- Know proton number identifies an element.
- Know the three emission types.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What happens to element identity in alpha decay?
What you will learn
- Use changing nuclear proton number to identify when radioactive decay changes an element.
- Connect alpha and beta-minus element changes to nuclear proton number.
Follow element identity
The proton number identifies an element. Alpha emission removes two protons and two neutrons from a parent nucleus, so its proton number decreases by two and the daughter is a different element. Beta-minus emission changes a neutron into a proton and emits an electron, increasing proton number by one.
Gamma emission changes nuclear energy without changing proton number. It therefore does not by itself change the element. These are nuclear processes, unlike adding or removing electrons around an unchanged nucleus.
Keep the beta electron in the correct account
The beta-minus electron is emitted in the nuclear change; it is not simply an orbital electron knocked off an atom. The simplified description here tracks the particles required for this syllabus. More complete particle accounts include another emitted particle in beta-minus decay.
Use supplied element labels or proton numbers to identify parents and daughters. The fact that an emission changes the element does not prove that the daughter has become non-radioactive.
Sources for this lesson
Pause and explain
Which listed emission leaves proton number unchanged?
Worked example
A supplied parent has proton number 6 and undergoes beta-minus decay. Does its element change?
Show the worked solution
- Beta-minus raises the nuclear proton count by one.
- The daughter has proton number 7.
- Different proton numbers identify different elements.
Answer Yes: the daughter is a different element with proton number 7.
Try a topic test
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A nucleus with proton number 88 emits alpha. Find the daughter proton number.
Give me a hint
Account for the two emitted protons.
Compare my reasoning
- Start with 88.
- Two protons leave.
- The daughter has 86.
86; a different element.
Look for these in your work
- Subtract two.
- Link proton number to element.
A nucleus with proton number 6 emits beta-minus. Find the daughter proton number.
Give me a hint
Use neutron-to-proton change.
Compare my reasoning
- One neutron becomes a proton.
- The proton count rises by one.
- It becomes 7.
7; a different element.
Look for these in your work
- Increase by one.
- Do not treat beta as orbital loss.
A gamma emission is described as turning carbon into nitrogen. Evaluate the claim.
Give me a hint
Check whether proton number changes.
Compare my reasoning
- Gamma changes nuclear energy.
- The proton number stays the same.
- The element stays carbon.
Gamma alone does not turn carbon into nitrogen.
Look for these in your work
- Use the nuclear proton account.
- Separate energy and element identity.
Common mistakes
- Element identity follows protons.
- Beta emission is not orbital-electron removal.
- Gamma does not change proton number.
What can you explain now?
What identifies an element?
Compare with the explanation
Proton number
The number of protons in the nucleus identifies the element.
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Make it stick
Connect alpha and beta-minus element changes to nuclear proton number.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.