Calculate the mass defect (in g/mol) and the binding energy (in MeV/nucleon) for the following nuclei. Which of the two is more stable? (a) 7Li (atomic mass = 7.016004) (b) 39K (atomic mass = 38.963706)

The mass defect is the difference between the mass of an atomic nucleus and the sum of the individual masses of its protons and neutrons. This discrepancy arises because some mass is converted into energy during the formation of the nucleus, according to Einstein's equation E=mc². The mass defect is crucial for understanding nuclear stability and is typically expressed in atomic mass units (u) or grams per mole (g/mol).

Binding energy is the energy required to disassemble a nucleus into its constituent protons and neutrons. It is directly related to the mass defect, as the energy equivalent of the mass defect represents the binding energy of the nucleus. Binding energy is often expressed in mega-electronvolts per nucleon (MeV/nucleon), providing insight into the stability of the nucleus; a higher binding energy indicates a more stable nucleus.

Nuclear stability refers to the ability of a nucleus to remain intact without undergoing radioactive decay. It is influenced by the balance between the attractive nuclear force, which holds protons and neutrons together, and the repulsive electromagnetic force between protons. Nuclei with higher binding energies per nucleon are generally more stable, as they are less likely to break apart, making the comparison of binding energies essential for assessing stability.