Chemistry
Atom Calculator (Neutrons)
Find the number of neutrons from mass number and atomic number.
Free to use — no sign-up or login.
Neutrons (N)
Protons
Electrons (neutral atom)
Amortization schedule
| # | Date | Payment | Principal | Extra | Interest | Balance |
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Neutron number is the mass number minus the atomic number: N = A − Z. A counts protons and neutrons together. Z counts protons.
The proton calculator stops at Z. This page needs both A and Z, and it draws a neutral atom with Z electrons.
What A and Z mean
A is a whole mass number for one isotope. Z is the atomic number and does not change between isotopes of the same element. Carbon is always Z = 6; carbon-12 and carbon-14 differ in A, and therefore in N.
Why a non-integer or A below Z is refused
A and Z are counts, so 6.5 is not a mass number here. A cannot be smaller than Z, because that would mean a negative neutron count. The sketch caps the dots and labels the rest so a heavy nucleus stays readable.
Worked example: carbon-12
Enter A = 12 and Z = 6. N = 12 − 6 = 6. The page also shows 6 protons and 6 electrons for a neutral atom.
\[ N = A - Z = 12 - 6 = 6 \]
Frequently asked questions
What is the neutron number?
N = A − Z, the neutrons in that isotope.
Does this page accept decimals?
No. A and Z must be whole numbers of 1 or more.
What if A is less than Z?
The calculator stops. Neutron count cannot be negative.
How many electrons does it draw?
A neutral atom is drawn with Z electrons, the same count as the protons.
Is uranium drawn dot by dot?
No. After a small cap, the sketch says how many more protons or neutrons remain.
References
Assumptions and limitations
Chemistry calculators are for study and illustration, not laboratory procedure or safety guidance. Confirm units, significant figures, and protocols from primary references before any practical work.
This is a count for one isotope, not a nuclear mass, binding energy, or ion charge. A charged ion would not have Z electrons.