What is the difference between the mass of an atom and the sum of the masses of its protons and neutrons called?

What is the difference between the mass of an atom and the sum of the masses of its protons and neutrons called?

• A. Nuclear Fertile Elements
• B. Decay Constant
• C. Common fissionable fuels
• D. Mass defect

Answer: (D)

The difference you’re being tested on is the mass defect. When a nucleus forms from protons and neutrons, the total mass of the separate particles ends up slightly larger than the mass of the bound nucleus. That missing mass isn’t lost—it’s converted into binding energy that holds the nucleus together, thanks to E = mc^2. So the mass defect is the amount by which the sum of the individual nucle masses exceeds the actual nuclear mass, and it corresponds to the binding energy of the nucleus. This energy is what makes nuclei stable, and the size of the defect (and thus the binding energy) varies with the nucleus. If you’re comparing atomic mass to the sum of protons and neutrons, the electron masses are a small added factor, but the underlying idea remains the same: the mass difference reflects the energy binding the nucleus together.

The difference you’re being tested on is the mass defect. When a nucleus forms from protons and neutrons, the total mass of the separate particles ends up slightly larger than the mass of the bound nucleus. That missing mass isn’t lost—it’s converted into binding energy that holds the nucleus together, thanks to E = mc^2. So the mass defect is the amount by which the sum of the individual nucle masses exceeds the actual nuclear mass, and it corresponds to the binding energy of the nucleus. This energy is what makes nuclei stable, and the size of the defect (and thus the binding energy) varies with the nucleus. If you’re comparing atomic mass to the sum of protons and neutrons, the electron masses are a small added factor, but the underlying idea remains the same: the mass difference reflects the energy binding the nucleus together.