What does the sum of the protons and neutrons in an atom equal?

1 Answer
Apr 6, 2017

Answer:

The Atomic mass number.

Explanation:

In an atom, almost all of its mass is contributed my protons and neutrons. Electrons do not contribute much to the mass of that atom because its mass is negligible compared to that of protons and neutrons.

The mass of protons and neutrons are almost equal are are taken to be approximately 1 amu (atomic mass unit).

So the mass of an atom is the mass of the protons and neutrons in it.

This is why the sum of the number of protons and neutrons in an atom equals its atomic mass number.