Mass Defect

Mass Defect

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. When a nucleus is formed, some of the mass is converted into energy in order to binding the nucleons. This converted energy is called binding energy. Due to this conversion of mass into energy, mass decreased and result as 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 mass defect (𝚫M) can be calculated by subtracting the original atomic mass (M_A) from the sum of the mass of protons (m_p = 1.00728 amu) and neutrons (m_n = 1.00867 amu) present in the nucleus.
𝚫M = (Zm_p + Nm_n) – M_A
𝚫M – mass defect
M_A – mass of the nucleus
m_p – mass of a proton, i.e. 1.00728 amu
m_n – mass of a neutron, i.e. 1.00867 amu
Z – number of protons
N – number of neutrons

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