Calculation Inputs
Choose a mode and provide nuclear data. The calculator finds the mass number, protons, or neutrons for a selected isotope. Use presets to explore common nuclides instantly.
Isotope series generator
Build a sequence of isotopes for one element by keeping protons fixed and sweeping neutron counts. Compare how mass number and neutron-to-proton ratio evolve across the series.
Example mass numbers for common isotopes
The table below lists selected nuclides showing how protons and neutrons combine to give the integer mass number A.
| Element | Symbol | Protons (Z) | Neutrons (N) | Mass number (A) | Isotope notation |
|---|---|---|---|---|---|
| Hydrogen-1 | H | 1 | 0 | 1 | 1H |
| Carbon-12 | C | 6 | 6 | 12 | 12C |
| Oxygen-16 | O | 8 | 8 | 16 | 16O |
| Uranium-238 | U | 92 | 146 | 238 | 238U |
Formula used in this calculator
The mass number A of a nuclide is defined as the total number of nucleons, that is, the sum of the number of protons Z and neutrons N:
A = Z + N
From this definition, two rearranged forms are directly obtained:
- N = A − Z — calculate neutrons from mass number and protons.
- Z = A − N — calculate protons from mass number and neutrons.
The calculator implements these integer relationships, ensuring mass number remains a whole number and consistent with the entered nuclear composition.
How to use this calculator
- Select the single isotope mode or the series generator.
- Use a preset isotope or enter the nuclear data manually.
- Provide protons, neutrons, and mass number as required by the mode.
- Run the calculation to generate a numeric and textual summary.
- Interpret classification, N/Z ratio, and stability comments for insight.
- Export results or series to CSV or PDF for reports and assignments.
Ensure all nuclear counts are non-negative whole numbers for meaningful, physically realistic calculations and comparisons.
Mass number and atomic composition
Mass number counts all protons and neutrons in a nucleus. This tool lets you explore how changing neutron count produces isotopes of the same element, alongside composition views in the Advanced Atom Calculator.
Comparing mass number with atomic mass
Mass number is an integer value for a specific nuclide, whereas atomic mass is a weighted average over isotopes. Compare individual nuclides calculated here with averaged values from the Atomic Mass Calculator when building reference tables or lesson notes.
Using mass number with mole and atom calculations
After identifying a nuclide using its mass number, you can connect nuclear information to macroscale quantities. Combine this page with the Number of Atoms in a Mole Calculator to move between nuclei, moles, and total atoms in a sample.
Neutron-to-proton ratio and nuclear stability
The calculator reports the neutron-to-proton ratio and a short stability comment for each nuclide. These values help students see how very low or very high ratios often correspond to unstable nuclei outside the typical band of stability on N versus Z charts.
Exploring isotope series for one element
The isotope series generator keeps proton number fixed and sweeps a range of neutron counts. This produces tables of candidate isotopes, complete with mass numbers, N/Z ratios, and stability hints useful for workshops on nuclide charts and nuclear notation practice.
Exporting nuclear data for reports and assignments
Both single-nuclide results and isotope series can be exported as CSV or PDF files. Learners may attach these summaries to lab reports, homework solutions, or digital notebooks to show intermediate nuclear calculations clearly and consistently.
Frequently asked questions
What is the mass number of an atom?
Mass number is the total count of protons and neutrons in a nucleus. This page lets you calculate it or recover missing nuclear counts, using the simple integer relationships between A, Z, and N for any single nuclide.
How is mass number different from atomic mass?
Mass number is always an integer for one nuclide. Atomic mass is a weighted average across naturally occurring isotopes. For detailed average values and isotope tables, use the Atomic Mass Calculator alongside this mass number tool.
Can this calculator tell me if an isotope is stable?
It estimates stability qualitatively using the neutron-to-proton ratio, highlighting neutron-rich or proton-rich compositions. However, it does not replace full nuclear data tables, which list experimentally known stable and radioactive nuclides.
What should I enter if I only know A and Z?
Select the mode that computes neutrons from mass number and protons. Enter A and Z, and the tool finds N and updates the isotope notation, classification, and neutron-to-proton ratio automatically for that nuclide.
How do I generate a full isotope table for one element?
Use the isotope series generator section. Enter the element symbol, a fixed proton number, and minimum and maximum neutron counts. The calculator builds a table you can export as CSV or PDF for classroom discussions or assignments.
Can I use this for molecules or ions?
The tool focuses on individual nuclei, so it does not parse whole molecular formulas. For molecule-based atom counts, pair these nuclear results with formula-aware tools such as the Advanced Atom Calculator or Number of Atoms in a Mole Calculator.
Is this calculator suitable for exams and lab reports?
It is designed as a teaching and revision aid. You can export tables and cite them in lab reports, but always cross-check results with course materials or textbooks before using numbers in graded work or formal documents.