Binding Energy per Nucleon and Stability Curve
Average binding energy per nucleon is B/A. Its curve rises steeply for light nuclei, peaks near iron-nickel mass numbers, and decreases slowly for heavy nuclei; a larger value usually indicates greater resistance to separation, not immunity to every decay.
Why this shows up in the exam
Ordering nuclear stability · Predicting exothermic fusion or fission · Estimating reaction energy from tabulated B/A
Learn the idea
Binding energy per nucleon measures average binding and explains why fusion and fission can both release energy. Nuclei move toward more tightly bound products. Light nuclei can gain average binding by joining, while very heavy nuclei can gain it by splitting into medium-mass fragments.
🧠 Memory hook: Products higher on B per A release the difference.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- average binding = B/A — total binding energy divided by nucleon count
- Q = B_products - B_reactants — reaction energy from total bindings when nucleon content is conserved
How to approach it
- 1Convert every B/A value to total B
- 2Subtract reactant total binding from product total binding
- 3Use the sign to decide release or supply
Common slip-ups that cost marks
- •Comparing B/A without multiplying by A when total energy is needed
- •Claiming B/A increases for every heavier nucleus
- •Treating the curve as perfectly smooth for individual nuclides
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
In hydrogen, an electron transitions from n = 2 to n = 1. Using E_n = -13.6/n^2 eV, find the emitted photon energy.
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