Calculate the mass defect for He-4 given the following masses: proton 1.0073 amu; neutron 1.0087 amu; electron 0.0005 amu; He-4 mass 4.0026 amu. He-4 has 2 protons, 2 neutrons, and 2 electrons.

Calculate the mass defect for He-4 given the following masses: proton 1.0073 amu; neutron 1.0087 amu; electron 0.0005 amu; He-4 mass 4.0026 amu. He-4 has 2 protons, 2 neutrons, and 2 electrons.

• A. 0.003038 amu
• B. 0.03038 amu
• C. 0.3038 amu
• D. 0.0003038 amu

Answer: (B)

Mass defect shows how much mass is converted into binding energy when a nucleus forms. For a helium-4 atom, consider the masses of its separate parts: two protons, two neutrons, and two electrons. Using the given values, the total mass of these constituents is 2×1.0073 + 2×1.0087 + 2×0.0005 = 4.0330 amu. The actual mass of the neutral helium-4 atom is 4.0026 amu. The mass defect is the difference: 4.0330 − 4.0026 ≈ 0.0304 amu, which is about 0.03038 amu. This deficit corresponds to the binding energy that holds the nucleus together via E = Δm c^2.

Mass defect shows how much mass is converted into binding energy when a nucleus forms. For a helium-4 atom, consider the masses of its separate parts: two protons, two neutrons, and two electrons. Using the given values, the total mass of these constituents is 2×1.0073 + 2×1.0087 + 2×0.0005 = 4.0330 amu. The actual mass of the neutral helium-4 atom is 4.0026 amu. The mass defect is the difference: 4.0330 − 4.0026 ≈ 0.0304 amu, which is about 0.03038 amu. This deficit corresponds to the binding energy that holds the nucleus together via E = Δm c^2.