What is mass defect?

What is mass defect?

• A. The energy required to remove electrons from an atom
• B. The difference between the mass of the atom and the sum of the masses of its constituent particles
• C. The total mass of the atom
• D. The energy released when electrons are added

Answer: (B)

Mass defect is the difference between the mass of a bound system and the sum of the masses of its parts when unbound. When nuclei form from protons and neutrons (and, for atoms, including electrons), the bound system weighs less. That missing mass has been converted into binding energy, via E = mc^2, which holds the nucleus together. So the mass defect is essentially the difference between the actual mass of the atom (or nucleus) and the total mass of its constituent particles. The other statements describe ionization energy, the total mass itself, or energy changes from adding electrons, which aren’t what mass defect means.

Mass defect is the difference between the mass of a bound system and the sum of the masses of its parts when unbound. When nuclei form from protons and neutrons (and, for atoms, including electrons), the bound system weighs less. That missing mass has been converted into binding energy, via E = mc^2, which holds the nucleus together. So the mass defect is essentially the difference between the actual mass of the atom (or nucleus) and the total mass of its constituent particles. The other statements describe ionization energy, the total mass itself, or energy changes from adding electrons, which aren’t what mass defect means.