I keep getting “Filling rules” questions wrong in Structure of Atom. What's the trap?
pairing electrons in a subshell before every orbital has one.
The usual trap: pairing electrons in a subshell before every orbital has one. How to avoid it: fill each orbital singly with parallel spins first, then pair up. Go back to the definition — Aufbau (lowest energy first), Pauli (max two electrons, opposite spins) and Hund (singly fill before pairing).
Key point
Filling rules
Common mistake
pairing electrons in a subshell before every orbital has one.
Memory tip
fill each orbital singly with parallel spins first, then pair up.
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