# How do you figure out the number of neutrons in a atom?

enotechris | College Teacher | (Level 2) Senior Educator

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Atoms can have a variable number of neutrons.  That is why the atomic mass is not a whole number; it represents an average weight of all the atoms of an element, which may have different numbers of neutrons. An atom always has the same number of protons, but may have many different numbers of neutrons in the nucleus.  Each of these is known as an isotope of the atom.  So, an atom's proton count always remains the same, but its neutron count may vary.  The second link shows a Periodic Table of Isotopes.  Who knew that hydrogen can have up to 5 neutrons in its nucleus!

pohnpei397 | College Teacher | (Level 3) Distinguished Educator

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Atoms are all made up of three kinds of subatomic particles.  These are electrons, which have negative charges, protons, which have positive charges, and neutrons, which are neutral.  The protons and neutrons make up the nucleus of the atom while the electrons orbit the nucleus.

In order to find the number of neutrons in an atom, take the following steps:

1.  Look up the element on the Periodic Table.

2.  Find the atomic number.

3.  Find the atomic weight.

4.  Round the atomic weight to the nearest whole number.  This tells you the atomic mass.

5.  Subtract the atomic number from the atomic mass.  This gives you the number of neutrons in the atom.

atyourservice | Student, Grade 11 | (Level 3) Valedictorian

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atomic mass - atomic number = neutrons

canyousee67 | Student, Grade 9 | (Level 1) eNoter

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You must find out the Atomic Number and Atomic mass of an element. Lastly, you subtract the atomis# from the atomic mass.