The mass defect of an atom refers to the difference in mass between an atom and the sum of the masses of its individual protons, neutrons, and electrons. It arises due to the binding energy that holds the nucleus of an atom together.
According to Einstein's mass-energy equivalence principle (E=mc²), mass and energy are interchangeable. In the context of atomic nuclei, the strong nuclear force binds protons and neutrons together, overcoming the electrostatic repulsion between positively charged protons. This binding process releases energy, which corresponds to a decrease in mass.
The mass defect is a measure of this lost mass, which is converted into binding energy according to the equation ΔE = Δmc², where ΔE represents the energy released, Δm is the mass defect, and c is the speed of light.
The mass defect is typically expressed in atomic mass units (u) or kilograms (kg). It is important in nuclear physics and is often used to calculate the binding energy per nucleon (proton or neutron) in a nucleus. The higher the binding energy per nucleon, the more stable the nucleus is.
The concept of mass defect is closely related to nuclear reactions, such as nuclear fission (splitting of atomic nuclei) and nuclear fusion (combining of atomic nuclei), where the difference in mass before and after the reaction is used to calculate the released or absorbed energy.
In summary, the mass defect of an atom represents the difference in mass between the combined particles within the nucleus and the actual mass of the atom, resulting from the conversion of mass to binding energy.