Write and explain beta-minus decay equations
Track neutron-to-proton conversion and balance the emitted electron charge number.
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
- Read signed charge labels.
- Know neutron and proton identities.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which nuclear conversion describes beta-minus?
What you will learn
- Track neutron-to-proton conversion and balance the emitted electron charge number.
- Explain and balance beta-minus equations while recognising their simplified particle scope.
Preserve nucleon number and change proton number
In beta-minus decay a neutron becomes a proton and an electron is emitted. The daughter A is unchanged, Z increases by one and neutron number decreases by one. The emitted electron is written ⁰₋₁e, so ¹⁴₆C → ¹⁴₇N + ⁰₋₁e balances 14 = 14 + 0 and 6 = 7 − 1.
The emitted electron arises in the nuclear change. It was not a pre-existing electron orbiting the atom that simply escaped. This makes beta decay different from ordinary positive-ion formation.
Recognise the simplified particle account
The syllabus equation balances nucleon number and charge number. In the fuller physical beta-minus process an antineutrino is also emitted; it has zero nucleon number and zero electric charge, so it does not change these two balances. The simplified equation is not a complete account of energy and momentum.
A may stay the same even though the element changes because Z identifies the element. The daughter may be more stable without that alone proving it is permanently non-radioactive.
Sources for this lesson
Pause and explain
Why does the electron have A = 0 in a nuclide equation?
Worked example
Complete ¹⁴₆C → ? + ⁰₋₁e, given Z = 7 identifies N.
Show the worked solution
- Keep A = 14.
- Increase Z to 7.
- Check 7 − 1 = 6.
Answer ¹⁴₇N.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
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.
Write the syllabus beta-minus equation for ¹⁴₆C with daughter N.
Give me a hint
Keep A and balance Z with the emitted electron.
Compare my reasoning
- Daughter A is 14.
- Daughter Z is 7.
- The electron labels are 0 and −1.
¹⁴₆C → ¹⁴₇N + ⁰₋₁e.
Look for these in your work
- Balance 14 on both sides.
- Balance 6 = 7 − 1.
A parent has A = 24 and Z = 11. Find daughter A, Z and neutron number after beta-minus.
Give me a hint
Change one neutron into a proton.
Compare my reasoning
- A remains 24.
- Z becomes 12.
- Neutrons = 24 − 12 = 12.
A = 24; Z = 12; 12 neutrons.
Look for these in your work
- Keep nucleon count.
- Reduce neutron count by one.
A report says beta decay is a neutral atom losing an orbital electron. Correct the mechanism.
Give me a hint
Locate the changing particle in the nucleus.
Compare my reasoning
- A neutron becomes a proton.
- An electron is emitted in the nuclear change.
- Orbital-electron loss alone changes ion charge without this nuclear conversion.
Beta-minus is nuclear neutron-to-proton conversion, not ordinary ion formation.
Look for these in your work
- Locate the nuclear change.
- Distinguish ionisation.
Common mistakes
- Keep A unchanged.
- Beta electron is not orbital loss.
- Balance the negative electron label.
What can you explain now?
What is the charge number of a beta-minus electron?
Compare with the explanation
−1
The emitted electron carries one negative relative charge.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Explain and balance beta-minus equations while recognising their simplified particle scope.
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.