In an isotope, what determines the number?

For example Nitrogen-14 has 7 electrons, protons, and neutrons. Which two determine the 14 in Nitrogen-14? Thank you!

1 Answer

The number is determined by protons + neutrons


The 14 in Nitrogen-14 is the mass of this isotope of nitrogen.

For most chemistry classes you can consider the mass of a proton to be 1 amu and the mass of a neutron to also be 1 amu. There actually is a slight difference, but that difference is so small it is not important for the question you are asking.

The mass of an electron is almost 2000x smaller than the mass of a proton or neutron so we will treat electrons as though their mass is 0. See more info about mass of subatomic particles here .

So the mass of a particle that has 7 protons and 7 neutrons must be 14.

This video gives more explanation of how to work with the subatomic particles of isotopes.

Hope this helps!