Easy Practice — Set 2

Quick Recap — Configurations & Rules

• Energy order ($n+l$ rule): lower $(n+l)$ fills first; for a tie, the lower $n$ fills first — so $4s$ before $3d$.
• Half-filled/fully-filled stability gives the exceptions Cr $=[Ar]3d^5 4s^1$ and Cu $=[Ar]3d^{10}4s^1$.
• Nodes: radial $=n-l-1$, angular $=l$, total $=n-1$.
• Photon: $E=h\nu=\dfrac{hc}{\lambda}$; Heisenberg: $\Delta x\,\Delta p\ge\dfrac{h}{4\pi}$.