What this calculator does
Atom composition (protons, neutrons, electrons) works out subatomic particle counts from atomic number, mass number and charge. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
Formulaprotons = Z; neutrons = A − Z; electrons = Z − charge
The inputs explained
| Field | What to enter |
|---|---|
| Atomic number Z | A number. Starts at 17. |
| Mass number A | A number. Starts at 35. |
| Ion charge | A number. Starts at -1. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with atomic number z
Every other input is held at the calculator’s starting values while atomic number z varies. Select any row to load that scenario into the calculator.