Atomic & nuclear physics · Topic 17 of 17

Atomic Structure, Binding Energy & Nuclear Stability

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Physics · atomic & nuclear

The strong force holds nucleons together; a nucleus weighs less than its parts, and that missing mass is the binding energy, E = mc².

01 · Strong forceStrong force: strong, very short range

02 · Mass defectNucleus mass < sum of its parts

03 · Binding energyBinding energy E = Δm·c²

Strong force: holds nucleons together; very strong, very short range must know

Mass defect: a nucleus weighs less than its separate nucleons must know

Without the strong force, repelling protons would fly apart

Wrong neutron-to-proton balance → unstable → radioactive decay

Decay products weigh less; the lost mass leaves as radiation energy

Nucleus = protons (+) and neutrons (0); electrons (−) outside must know

Binding energy E = Δm·c²: energy to split a nucleus into nucleons must know

Mass number A = Z (protons) + N (neutrons)

Proton ≈ neutron ≈ 1 u; electron ≈ 1/1836 of a proton

More binding energy per nucleon = more stable nucleus

Stable light nuclei: neutrons ≈ protons

Stable heavy nuclei: more neutrons than protons

Δm = 2.0 × 10⁻²⁹ kg → E = 1.8 × 10⁻¹² J

Nucleons 6.0480 u, nucleus 6.0135 u → Δm = 0.0345 u

Commonly confused

	Strong nuclear force	Electric (Coulomb) force
Push or pull	Pulls nucleons together	Pushes protons apart
Acts on	Protons and neutrons	Charged protons only
Range	Very short (a few femtometers)	Long; weakens with distance squared
Up close	About 100 times stronger	Weaker
In heavy nuclei	Extra neutrons add more pull	Repulsion grows with every proton

Trap: binding energy must be ADDED to split a nucleus apart

Show 6 more facts

Nuclear energy per event ≈ 10⁶ × chemical (MeV vs eV)

Binding energy per nucleon peaks near iron (A ≈ 60), about 8 MeV

Fusion of light / fission of heavy nuclei release energy (toward iron)

Even proton and neutron counts and magic numbers → extra stable

1 u of mass = 931.5 MeV of energy

Δm = 0.0345 u → binding energy ≈ 32.1 MeV

Pearl

A nucleus weighs less than its parts; the missing mass times c² is its binding energy.

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