Read and write labelled nuclide notation
Place mass number above proton number and keep isotope notation separate from ion charge.
Core and Extended; Physics 0625, 2026–2028. Use labelled nuclides, supplied count intervals and stated background conditions. Model drawings are not to scale. Written practice is self-checked.
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.
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.