# Protons, Neutrons, and Electrons

1. I have $$^{9}$$Be$$^{+}$$, $$^{12}$$C, and $$^{15}$$N$$^{+++}$$ isotopes, and I need to find the total of protons, neutrons, and electrons.

A = Z + N, where A is the atomic mass number and Z is the number of protons and N is the number of Neutrons.

3. I know this is an easy question, I put it in physics because they asked me this in my physics class. For beryllium, I think there is ONE less electron right? Normally it would be four since there are four protons, so then there are three electrons, three protons and 6 neutrons? Since A is 9, for the others I am still weary, since I got this info online, I just want to know how to get this from the periodic table and just figure it out myself, thanks!

Last edited:

Tom Mattson
Staff Emeritus
Gold Member
For beryllium, I think there is ONE less electron right? Normally it would be four since there are four protons, so then there are three electrons, three protons and 3 neutrons? Since A is 9,

Close. You're right about the protons and electrons. But you made a small subtraction error when calculating the number of neutrons. Try again?

for the others I am still weary, since I got this info online, I just want to know how to get this from the periodic table and just figure it out myself, thanks!

The only thing you need to know from the periodic table is the atomic number, which tells you the number of protons. You are given the value of A and the total charge on the isotope, so you can easily get the numbers of neutrons and electrons.

Ok, so N = A - Z, so 9 - 4 = 5 neutrons, 4 protons, and 3 electrons, thanks!

Tom Mattson
Staff Emeritus