Chemistry / Unit 12 Chem 2499 short lesson, about 20 seconds
Mass Defect and Nuclear Binding Energy
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The idea
A nucleus's mass defect is the gap between its particles' summed mass and measured mass; mass-energy equivalence converts that missing mass into binding energy.
In practice
A helium-4 nucleus measures slightly less than its separate protons and neutrons, the missing mass accounting for binding energy.
Where people slip
Mass-energy equivalence is a defining conversion, not a revisable measurement — the mass defect varies between nuclides.
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