Ch 5 The simplest atomic system: one proton and one electron interacting via the Coulomb potential $V(r) = -e^2/(4\pi\epsilon_0 r)$. Energy levels: $E_n = -13.6\,\text{eV}/n^2$. Quantum numbers: $n$ (principal), $l$ (orbital), $m$ (magnetic), $m_s$ (spin). The textbook's primary anchor example. *See