Question

How is an elements atomic mass determined

Answer 1

An element's mass is determined by  adding up the masses of protons and neutrons.

Answer 2

Another way to calculate the atomic mass of an element is to add up the masses of protons and neutrons. Example: Find the atomic mass of an isotope of carbon that has 7 neutrons. You can see from the periodic table that carbon has an atomic number of 6, which is its number of protons.