In nuclear chemistry, the mass defect of a nucleus can be calculated by following these steps:
1. Determine the actual mass of the nucleus in question. This mass is often measured in atomic mass units (u) and is a value determined through experimental observation.
2. Calculate the sum of the masses of the individual protons and neutrons that make up the nucleus. The number of protons is given by the atomic number of the element, and the number of neutrons is determined by subtracting the atomic number from the mass number (which is the total number of protons and neutrons).
3. Use the standard masses for protons and neutrons to calculate this sum. A proton and a neutron both have a mass approximately equal to 1 u (it is actually a little bit more, but for the mass defect, the approximate value will suffice for explanation). So, for element X with Z protons and N neutrons, the total mass of the protons and neutrons is approximately Z+N atomic mass units.
4. The 'mass defect' is found by subtracting the actual mass of the nucleus from the calculated sum of the individual masses of the protons and neutrons. This difference in mass arises because of the binding energy that holds the nucleus together according to Einstein's equation E=mc^2, where E is energy, m is mass, and c is the speed of light. Mass is essentially lost and converted into binding energy that holds the nucleus together.
Now, let's match this procedure with the options given in the question:
A) By subtracting the total number of neutrons from the total number of protons - This option simply describes the process of finding the number of protons (atomic number) and is not related to mass defect.
B) By dividing the total mass of the nucleus by the number of protons - This would give you an average mass per proton, which is not the mass defect.
C) By comparing the mass of the nucleus with the sum of the masses of its individual protons and neutrons - This matches the correct procedure for calculating the mass defect described above.
D) By adding the total number of protons and neutrons in the nucleus - This gives you the mass number, which is not the mass defect but instead the approximate sum of the masses sans the mass defect.
The correct option is C) By comparing the mass of the nucleus with the sum of the masses of its individual protons and neutrons.
