why is it that in finding the mass no. of an element, we are going to add the no. of protons with its neutrons

Question

I'm just conscious so i ask this question because there were no details in my book about the formulation of the equation...i will wait for your answers, those who wants to answer me....please.........................................................................................................................................................................................................................................i want to figure it out................................................................................................................................................................................................................................................i need answers.................................................................................................................................................................................../////////////////////////...............................................................................................

Answer 1

The atomic Mass of an Element is pretty much the weight of an atom. In an atom, we have protons, Neutrons, and Electrons (without going into quarks and whatnot). The Protons and the Neutrons both have a mass of 1 a.m.u. (atomic mass unit). An electron doesn't weigh much at all, and in basic secondary school's the weight is negligable.
With the electrons considered 0 (but they aren't), we just add the mass of the protons, and the mass of the neutrons, which are 1.
Since 1 (1 a.m.u.) x the number of protons + 1 (1 a.m.u.) x the number of neutrons, is the same as the protons plus neutrons, we can add them to get the mass number.

Answer 2

The protons and the neutrons have the hardly the same mass.

Answer 3

technically, the bulk of the volume of an atom is due to the nucleus and only the nuclear particles, the neutrons and protons, are massive...relatively, the mass of the electrons are negligible:)