Explanation: Some atoms don't 'need' neutrons The hydrogen atom does not have any neutrons. However, as # of protons increases, the number of neutrons increases as well. Naturally, 'positive charges repel', so it wouldn't be possible to have more than one proton in the nucleus.
The number of protons in each atom is also it's atomic number on the periodic table, meaning each pure element has a different number of protons. You can tell how many neutrons are in an atom by looking at the atomic mass, which is protons + neutrons = atomic mass.
You are given the protons in the atomic number so take that minus the atomic mass to get the number of neutrons.
