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 always less than the predicted mass calculated by adding the individual masses of its constituent nucleons. When a nucleus is formed, some of the initial mass is converted into energy in order to bind the nucleons together. This converted energy is known as the binding energy. Due to this conversion of mass into energy, the total mass decreases, resulting in a mass defect. Because of this phenomenon, the actual mass of an atomic nucleus is invariably less than the combined mass of the isolated particles it is made up of.

Read Nuclear Binding Energy

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 – Actual mass of the nucleus
• m_p – Mass of a proton (approx. 1.00728 amu)
• m_n – Mass of a neutron (approx. 1.00867 amu)
• Z – Number of protons (Atomic number)
• N – Number of neutrons