Electronic Configuration

Electronic Configuration of Group 13

Every Group 13 element has the same outer (valence) configuration, $ns^2np^1$. But their inner cores are progressively more complicated on descending the group, and it is this hidden complexity — not the visible valence shell — that drives most of the group's irregular trends:

• Boron — core $[He]$: a simple noble-gas core with no d or f electrons underneath.
• Aluminium — core $[Ne]$: again a simple noble-gas core.
• Gallium — core $[Ar]3d^{10}$: a noble-gas core PLUS a full set of 10 d-electrons.
• Indium — core $[Kr]4d^{10}$: same pattern, one period down.
• Thallium — core $[Xe]4f^{14}5d^{10}$: a noble-gas core plus a full f-subshell AND a full d-subshell. …