How do you figure out how many neutrons are in a a atom?

Answer 1

Each nucleon (proton or neutron) contributes about 1 Atomic Mass unit to the mass of the atom. The mass contribution of the electrons can be ignored, since it takes about 1800 of them to equal the mass of a nucleon and the heaviest elements known have around 1/15th that number of electrons.

So if you subtract the atomic number (number of protons) from the atomic mass rounded to the nearest whole number (number of nucleons), what's left is the number of neutrons.

Answer 2

You can calculate the number of neutrons in an atom by subtracting the number of protons (which is equal to the atomic number) from the atomic mass of the atom. Atomic mass minus atomic number = number of neutrons.

Answer 3

No. of Neutrons = A-Z where A is mass number of the element and Z is the atomic no. of the element.