mass defect

Mass defect refers to the difference between the total mass of individual protons and neutrons in an atom’s nucleus and the actual mass of the nucleus itself. When these particles come together to form the nucleus, some of their mass is converted into energy, releasing it as binding energy that holds the nucleus together. This loss of mass is what we call the mass defect. It explains why the nucleus is slightly lighter than the sum of its parts and is fundamental to understanding nuclear reactions and the energy they produce.