⁵⁶₂₆Fe³⁺
- Protons
- 26
- Neutrons
- 30
- Electrons
- 23
- Nucleons
- 56
- Protons = atomic number of Iron =
26 - Neutrons = mass number − protons = 56 − 26 =
30 - Electrons = protons − charge = 26 − (3) =
23
Iron-56 is a stable isotope. Stable isotopes of Iron: 54, 56, 57, 58. More about Iron →
How it works
Protons = Z (the atomic number). Neutrons = A − Z, where A is the mass number. Electrons = Z − charge, so positive ions have fewer electrons than protons and negative ions have more.
The isotope check uses the same IAEA nuclide data as the element pages. If you enter a mass number that has never been observed for that element, the calculator tells you so.
Frequently asked questions
- How do I find the number of protons?
- The number of protons equals the atomic number, Z. Every iron atom has 26 protons; an atom with 27 protons is cobalt, not iron.
- How do I find the number of neutrons?
- Subtract the atomic number from the mass number: N = A − Z. Iron-56 has 56 − 26 = 30 neutrons.
- How many electrons does an ion have?
- Subtract the charge from the number of protons. Fe³⁺ has 26 − 3 = 23 electrons; Cl⁻ has 17 − (−1) = 18 electrons. A neutral atom has as many electrons as protons.
- Why can’t I use the atomic mass from the periodic table as the mass number?
- The atomic mass (55.845 for iron) is a weighted average over all natural isotopes, so it is not a whole number. The mass number of a single isotope is always a whole number. Rounding the atomic mass gives the most common mass number for most light elements, but not always.
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