Identify nuclear particles and their relative charges
Distinguish protons and neutrons inside the nucleus from surrounding electrons.
Exam scope and assessment notes
Core and Extended · Physics 0972, 2026–2028. Use labelled nuclides, supplied count intervals and stated background conditions. Model drawings are not to scale. Written practice is self-checked. Human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0972 has the same subject content as IGCSE 0625, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Know atomic regions.
- Add small whole-number counts.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is a neutron’s relative charge?
What you will learn
- Distinguish protons and neutrons inside the nucleus from surrounding electrons.
- Locate nuclear constituents and use the three relative particle charges correctly.
Build the nuclear inventory
A nucleus contains protons and neutrons, collectively called nucleons. A proton has relative charge +1 and a neutron has relative charge 0. Electrons have relative charge −1 and belong to the surrounding atomic region rather than the nuclear inventory in this model. A neutron is uncharged, not absent.
A nucleus containing three protons and four neutrons has seven nucleons and relative nuclear charge +3. Its charge is not +7: only protons contribute positive nuclear charge. The hydrogen-1 nucleus is the useful exception to any claim that every nucleus must contain a neutron; it contains one proton and no neutrons.
Keep component counts separate
Adding electrons to an atom can change its overall charge without changing the nucleus. A neutral atom with three protons has three electrons; its neutral total does not make the nucleus neutral. The nucleus still has positive charge.
Particle symbols and coloured circles in a drawing are a key, not measured particle colours or a literal packing arrangement. When asked for nucleus composition, report protons and neutrons. When asked for atomic or ionic charge, also account for surrounding electrons.
Pause and explain
Does a neutral atom have a neutral nucleus?
Worked example
A supplied nucleus contains three protons and four neutrons. Find nucleon count and relative nuclear charge.
Show the worked solution
- Both protons and neutrons are nucleons.
- Three plus four gives seven.
- Only the three protons contribute charge.
Answer 7 nucleons; nuclear charge +3.
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.
List relative charges of proton, neutron and electron.
Give me a hint
Associate each name with its signed charge.
Compare my reasoning
- A proton contributes +1.
- A neutron contributes 0.
- An electron contributes −1.
Proton +1; neutron 0; electron −1.
Look for these in your work
- Name all three.
- Retain signs and zero.
A nucleus has five protons and six neutrons. State its constituents and nucleon total.
Give me a hint
Count both types in the nucleus.
Compare my reasoning
- There are five protons.
- There are six neutrons.
- Their total is eleven nucleons.
5 protons, 6 neutrons; 11 nucleons.
Look for these in your work
- Exclude atomic electrons.
- Add the two nuclear counts.
A report says hydrogen-1 cannot have a nucleus because it has no neutrons. Correct it.
Give me a hint
A nucleus need not contain both types in every isotope.
Compare my reasoning
- Hydrogen-1 contains one proton.
- Its nucleus has zero neutrons.
- That proton is its positively charged nucleus.
Hydrogen-1 has a one-proton nucleus with no neutrons.
Look for these in your work
- Identify the exception.
- Do not remove the nucleus when neutron count is zero.
Common mistakes
- Neutrons have zero charge.
- Electrons are outside this nuclear inventory.
- Neutral atoms can have charged nuclei.
What can you explain now?
Which particles are nucleons?
Compare with the explanation
Protons and neutrons
Both nuclear constituents count toward the nucleus’s nucleon number.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Locate nuclear constituents and use the three relative particle charges correctly.
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.