What is the mass defect of a Carbon atom?
A carbon 12 atom has a mass defect of .098931 u. This number, the mass defect, represents the binding energy of the nucleus of the nucleus of the atom, and how energy has to be used to split this nucleus.
If you add the exact mass of the protons, neutrons, and electrons in an atom you do not get the exact atomic mass of the isotope. The diference is called the mass defect. The difference between the mass of the atomic nucleus and the sum of the masses of the particles within the nucleus is known as the mass defect.