I am trying to wrap my head around the relationship between binding energy and mass defect. I have read that the difference between the binding energies of the products and reactants of a nuclear equation is equal to the energy equivalent of the mass defect. Using this, along with exact masses of a proton, electron and deuteron I have calculated the following:
mass difference = 7.49089 x 10^-31 kg
Converting this mass to energy via E = mc^2
E = 6.732476 x 10^-14 J = 0.420208 MeV
This value is far from the value I have managed to find on the internet, which states that the binding energy of deuteron is approximately 2.2 MeV.
Am I wrong in my knowledge that the binding energy is equivalent to the mass defect, or is there some other explanation for the disparity in the binding energy I calculated and the value found on the internet?