Read and write labelled nuclide notation
Place mass number above proton number and keep isotope notation separate from ion charge.
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Define A and Z.
- Know electron transfer leaves nuclei unchanged.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
In ²⁴₁₂Mg, which number is the nucleon total?
What you will learn
- Place mass number above proton number and keep isotope notation separate from ion charge.
- Use the upper and lower nuclide numbers while preserving separate atom or ion charge.
Read the two left-hand numbers
Nuclide notation writes A above Z to the left of the element symbol X. For ¹⁴₆C, A = 14 and Z = 6, so the nucleus has six protons and eight neutrons. The letter identifies the element and must agree with its proton number.
In this library a compact written form such as ¹⁴₆C preserves the upper mass number and lower proton number. A separately stated ion charge belongs to the whole atom or ion and does not replace either left-hand nuclear number. Read the positions before calculating.
Check a notation against its inventory
For a supplied magnesium nucleus with 12 protons and 12 neutrons, A = 24 and Z = 12, giving ²⁴₁₂Mg. A magnesium ion with two fewer electrons has the same nuclear notation; its +2 ion charge is additional information.
A wrong element symbol paired with Z is not a different notation convention. A swapped A and Z can imply impossible neutron counts. Check identity and constituent totals rather than copying number positions by appearance alone.
Sources for this lesson
Pause and explain
Does forming a magnesium ion by losing electrons change its A or Z?
Worked example
Read proton and neutron counts from ¹⁴₆C.
Show the worked solution
- The upper number is A = 14.
- The lower number is Z = 6.
- Neutrons equal 14 − 6 = 8.
Answer 6 protons; 8 neutrons.
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 nuclide notation for supplied magnesium with 12 protons and 12 neutrons.
Give me a hint
Find A and Z before placing them.
Compare my reasoning
- Z = 12.
- A = 12 + 12 = 24.
- Use the supplied Mg identity.
²⁴₁₂Mg.
Look for these in your work
- Place A above Z.
- Use Mg consistently.
Read the neutron count in ²³₁₁Na.
Give me a hint
Subtract the lower nuclear number from the upper.
Compare my reasoning
- A = 23.
- Z = 11.
- Neutrons equal 12.
12 neutrons.
Look for these in your work
- Read both positions.
- Report neutrons rather than nucleons.
A supplied carbon nucleus has Z = 6 but its label says ¹⁴₇C. Identify the inconsistency.
Give me a hint
The lower number must agree with element identity.
Compare my reasoning
- Carbon has six protons in the supplied case.
- The label instead gives seven.
- Retain A = 14 and correct Z to six.
The correct supplied notation is ¹⁴₆C.
Look for these in your work
- Check identity as well as number total.
- Do not change the given nucleus.
Common mistakes
- A is upper left.
- Z is lower left.
- Ion charge is separate.
What can you explain now?
Which number identifies the element?
Compare with the explanation
Proton number Z
The element is determined by nuclear proton count, not the neutron count.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Use the upper and lower nuclide numbers while preserving separate atom or ion charge.
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.