yeh you do need to calculate mass defect...dot point:
solve problems and analyse information to calculate the mass defect and energy released in natural transmutation and fission reactions
to calculate mass defect, find the total mass of the subatomic particles[electrons, protons and neutrons], then find the mass of the atom formed...mass defect is the difference in mass between the two...
dot point: explain the concept of mass defect using Einstein's equivalence between mass and energy
As the subatomic particles come together some of the mass is converted to energy, which is the binding energy to keep the neucleons together in the nucleus. Most of the mass loss comes from the neutrons and protons because they have more mass than the electrons.
Referring to Eintein's equation E=mc or in this case E=[mass defect]c the binding energy is the energy equal to the mass defect as the atom is formed.