Now before we can talk about mass defect, it's first important that we are able to determine our predicted mass. Now our predicted mass represents the mass of all subatomic particles within a given element, the number of neutrons, protons and electrons. Now recall that one atomic mass unit is equal to 1.66×10-27kg.

Doing this helps us to find a relative mass in atomic mass units for each one of our subatomic particles. Now remember we have our neutrons, protons and electrons. They're actual masses in kilograms. Are these values, and by utilizing this conversion factor we can find their relative masses.

Doing this, we'd see that our neutrons weigh 1.00866AMU, are protons weigh 1.00727AMU, and our electrons, which are the smallest, would only weigh 0.00055AMU. As we can see, the neutrons are just slightly larger or have slightly greater masses than our protons, and their masses are much greater than our electrons.

That's why a vast majority of the total mass of an atom is found within the nucleus where the protons and neutrons reside, right? So we learn how to calculate our predicted masses from these relative masses of our subatomic particles.