Mass defect is the difference between the actual atomic mass and the predicted mass calculated by adding the mass of protons and neutrons present in the nucleus. The actual atomic mass is less than the predicted mass calculated by adding the masses of nucleons. This additional mass is accounted for by binding energy that is released when a nucleus is formed. When a nucleus is formed, some of the mass is converted to energy and this results in the mass defect. Due to this reason, the actual mass of an atomic nucleus is less than the mass of particles it is made up of.
The actual mass of the atomic nucleus is always less than the mass of protons and neutrons present in the nucleus. When a nucleus is formed, energy is released. This energy is removed in the form of a reduction in total mass. This missing mass is known as the ‘mass defect’ and it accounts for the energy released.
The mass defect (𝚫M) can be calculated by subtracting the original atomic mass (MA) from the sum of the mass of protons (mp= 1.00728 amu) and neutrons (mn= 1.00867 amu) present in the nucleus.
Mass defect formula:
𝚫M = (Zmp + Nmn) – MA
𝚫M – mass defect
MA – mass of the nucleus
mp – mass of a proton, i.e. 1.00728 amu
mn – mass of a neutron, i.e. 1.00867 amu
Z – number of protons
N – number of neutrons
Nuclear Binding Energy
Nuclear binding energy is the energy required to split an atomic nucleus into its components. It is the energy equivalent to the mass defect.
Binding energy can be calculated by Einstein’s formula, E = mc2.
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