Nuclear forces: properties
Nuclear structure · Physics
Bohr atom
Interactive 3DElectrons orbit the nucleus in shells — switch element to see H, He and Li fill their shells.
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Study notes
Example: Calculate the binding energy of a helium‑4 nucleus (2 protons and 2 neutrons). 1. Find the mass of the nucleus: 2 protons (1.007825 u each) + 2 neutrons (1.008665 u each) = 2(1.007825) + 2(1.008665) = 4.032, u. 2. Find the mass of the separated particles: 2 protons + 2 neutrons = 4.032, u. 3. Mass defect Δm = mass of separated particles – mass of nucleus = 4.032 – 4.032 = 0.000, u (in this simplified example the masses cancel). 4. Convert mass defect to energy: E = Δm × c². Using 1 u = 931.5 MeV/c², E = 0.000 × 931.5 = 0 MeV. (In real calculations the mass of the nucleus is slightly less, giving a binding energy of about 28 MeV for helium‑4). 5. Interpretation: The positive binding energy means the nucleus is stable and requires energy to break apart.