No, the mass defect and the mass number of an element are not the same.
The mass number of an atom is the sum of the number of protons and neutrons in its nucleus. It is usually denoted by the symbol "A." The mass number represents the total number of nucleons (protons and neutrons) in an atom.
On the other hand, the mass defect refers to the difference in mass between a nucleus and the sum of the masses of its individual protons and neutrons. It is a measure of the binding energy of the nucleus. The mass defect is typically denoted by the symbol "Δm" or "Δm" and is usually expressed in atomic mass units (u) or kilograms (kg).
The mass defect arises from the conversion of mass into energy during the formation of a nucleus. According to Einstein's mass-energy equivalence principle (E = mc^2), a small amount of mass is converted into energy when nucleons come together to form a nucleus. This released energy is responsible for holding the nucleus together against the electrostatic repulsion between protons.
To calculate the mass defect, you can subtract the actual mass of the nucleus (measured experimentally) from the sum of the masses of its individual protons and neutrons (which can be calculated using the atomic masses of the individual particles).
In summary, the mass number represents the total number of nucleons in an atom, while the mass defect refers to the difference in mass between the actual mass of a nucleus and the sum of the masses of its individual protons and neutrons.