Here in this example question it says calculate the mass defect in atomic mass units for oxygen 16. Here we're given the atomic mass units for each of the three subatomic particles. Now the steps that we're going to use to find our mass defects are step one, define predicted mass. Find the number of subatomic particles within the isotope and add their masses together.

So here we're talking about oxygen. 16 Oxygen has an atomic number of 8. 8 represents a number of protons. It's neutral, so it also has 8 electrons. And then if we do 16 - 8, that gives us the number of neutrons, which is also eight. So we have eight across the board for our three subatomic particles. Here is each one of their atomic mass units. We'd multiply them each by their atomic mass unit and add up the totals together, right?

So for a proton it would be 8 * 1.00727 AMU, an electron is 8 * 0.00055 AMU, and for our neutron it's 8 * 1.00866 AMU. When we do all of that, our predicted mass comes out to be 16.13184 AMU. So Step 2, to find the nuclear mass, you're going to subtract the mass number by the combined mass of all the electrons. So the mass number is 16 for oxygen 16 and we minus our 8 electrons, each one of them having a mass of 0.00055 AMU. So that's 15.9956 AMU.

And then here use the calculated mass of step one and step 2 to determine the mass defect. Remember predicted mass minus our mass defect equals our nuclear mass. So just plug it in and solve for M. So predicted is 16.13184 and then nuclear is 15.9956. Subtract 16.13184. So here we're going to get negative M equals negative 0.13624 AMU. Divide both sides by -1. So our mass defect M equals 0.13624 AMU, so that will be our final answer for the isotope of oxygen 16.