Chemistry I / Lewis Structures, Formal Charge and Resonance
Practice question · Select all that apply

Which species genuinely break the octet rule, rather than merely looking unusual?

Hints
  1. Three fall short, exceed, or cannot pair; one is a textbook octet.
  2. Methane has exactly eight electrons around carbon, the rule working normally.
Show the answer
  • A. SF6\mathrm{SF_6}, with twelve electrons on sulfur
  • B. BF3\mathrm{BF_3}, with six electrons on boron
  • D. NO, with an odd number of electrons
Why

BF3 is an incomplete octet, SF6 an expanded one, and NO has an unpairable odd electron. Methane obeys the octet rule perfectly and is not an exception at all.

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