Atom Calculator
Use this atom calculator to move between atomic number, mass number, protons, neutrons, electrons, and ionic charge for neutral atoms or ions.
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Run the calculator.
What This Atom Calculator Helps You Do
This calculator compresses the basic bookkeeping of atomic structure into a single workflow, which is useful when you need to move quickly between classroom notation, isotope labels, and ion charge problems.
Instead of treating each relationship separately, the page shows how atomic number, mass number, and charge fit together so the result is easier to check and less likely to be lost in sign mistakes.
How to Calculate Atom Calculator
- Choose the input mode: Use either atomic number plus mass number plus charge, or enter proton, neutron, and electron counts directly.
- Enter whole-number particle counts: Atoms and ions are described with integer counts, so decimal values are not meaningful here.
- Read the full particle summary: The page returns every related quantity, including the ionic charge sign.
- Check charge direction: Positive charge means fewer electrons than protons, while negative charge means extra electrons.
Atom Calculator Formula
| Variable | Meaning | Unit |
|---|---|---|
| Z | Atomic number | count of protons |
| A | Mass number | protons + neutrons |
| p | Number of protons | count |
| n | Number of neutrons | count |
| e | Number of electrons | count |
Use the worked examples below to check how the formula behaves with real values. If the result looks unexpected, verify the unit assumptions and the meaning of each variable before interpreting the answer.
Worked Examples
- Atomic number: 11
- Mass number: 23
- Charge: 0
Result: p = 11, n = 12, e = 11.
A neutral sodium atom has the same number of protons and electrons.
- Atomic number: 17
- Mass number: 35
- Charge: -1
Result: p = 17, n = 18, e = 18.
A -1 ion has one more electron than proton count.
- Protons: 16
- Neutrons: 16
- Electrons: 18
Result: Z = 16, A = 32, charge = -2.
This sulfur example shows how extra electrons produce a negative ionic charge.
- Protons: 26
- Neutrons: 30
- Electrons: 24
Result: Z = 26, A = 56, charge = +2.
When electrons are missing relative to protons, the ion is positively charged.
How to Interpret Your Results
| Range | Meaning | Action |
|---|---|---|
| Charge = 0 | The atom is neutral. | Protons and electrons match exactly. |
| Charge > 0 | The species is a cation. | It has lost one or more electrons relative to the neutral atom. |
| Charge < 0 | The species is an anion. | It has gained one or more electrons relative to the neutral atom. |
Frequently Asked Questions
References
Last reviewed: March 2026