Find protons, neutrons and electrons from atomic number, mass number and ionic charge, with worked examples and input checks.
Method, examples and limits
Choose the atomic number Z, the isotope mass number A and the signed net charge q. The tool returns Z protons, A − Z neutrons and Z − q electrons. It accepts integer counts and rejects negative implied neutron or electron counts.
For neutral sodium-23, enter 11, 23 and 0 to obtain 11 protons, 12 neutrons and 11 electrons. For Ca²⁺ with A = 40, enter 20, 40 and +2: 20 protons, 20 neutrons and 18 electrons.
A valid arithmetic combination is not a prediction of a stable or observed isotope. Use an isotope mass number, rather than a decimal average atomic weight.
Worked learning guide
How to Find Protons, Neutrons and Electrons in Atoms and Ions
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Frequently asked questions
Does an ion have a different atomic number?
No. Ordinary ion formation changes electrons. Atomic number counts protons.
Can I enter a decimal mass number?
No. Mass number counts protons plus neutrons and is an integer.