How this calculator works
Atomic number counts protons and identifies the element. Mass number counts protons plus neutrons, while ionic charge counts protons minus electrons. Choose a starting set of three independent quantities. Whole-number counts are required. The arithmetic can describe unstable nuclides; it does not establish that an isotope or charge state exists.
Formula
Z = p; A = p + n; q = p - e. Therefore n = A - Z and e = Z - q.
Worked example
Carbon-14 with Z = 6 and q = 0 has six protons, eight neutrons and six electrons. A sodium ion with 11 protons, 12 neutrons and 10 electrons has A = 23 and charge +1.
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Frequently asked questions
Does a negative charge mean fewer electrons?
No. A charge of -1 means one more electron than proton.
Is mass number an atomic weight?
No. Mass number is an integer particle count. Atomic weight reflects isotope masses and abundance.
Can I identify an element from neutrons?
You also need mass number or another way to determine the proton count.