Theme E · Nuclear & Quantum Physics

$Z$ = protons, $A$ = nucleons, $N = A - Z$ = neutrons.

Same $Z$, different $N$ — same element, different mass.

electrons = protons = $Z$. An ion has electrons ≠ protons.

Proton (+e, in nucleus), neutron (0, in nucleus), electron (−e, $\approx 1/1836$ mass).

Electrons occupy discrete (quantised) energy levels around the nucleus.

Electrons jumping levels emit/absorb photons of specific frequencies → line spectra.

$h = 6.63\times10^{-34}$ J s; higher f ⇒ more energetic photon.

Convenient for atomic/nuclear energies; multiply eV by e to get joules.

Very short range, attractive — holds the nucleus together against proton–proton repulsion.

Geiger–Marsden (gold foil): most α pass through ⇒ atom is mostly empty; few bounce back ⇒ tiny dense + nucleus.

$E$: J (or eV) · $f$: Hz · $\lambda$: m · $Z,A,N$: counts (no unit).

Forgetting to convert eV→J before using SI formulas; mixing $Z$ (protons) and $A$ (nucleons).