Chemistry I / Lewis Structures, Formal Charge and Resonance
Practice question · Sort into groups

Sort each central atom by whether it can hold more than eight valence electrons.

Groups: Capped at eight · Can expand beyond eight

Hints
  1. Ask which period each element sits in.
  2. Only from period 3 downward is there room beyond eight.
Show the answer

Capped at eight: Nitrogen, Oxygen, Carbon

Can expand beyond eight: Phosphorus, Sulfur, Chlorine

Why

Period 2 elements have only 2s2s and 2p2p available and are capped at eight, which is why NF5 does not exist. From period 3 the atoms are larger and can accommodate more, giving real compounds such as PCl5\mathrm{PCl_5} and SF6\mathrm{SF_6}.

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