• Exceptions to the octet rule fall into one of three categories: (1) an incomplete octet, (2) odd-electron molecules, and (3) an expanded octet.
  • In some compounds, the number of electrons surrounding the central atom in a stable molecule is fewer than eight.
  • Beryllium hydride (BeH2) consists of two single covalent bonds between Be and H (see Figure below) In phosphorus pentachloride, the central phosphorus atom makes five single bonds to chlorine atoms and as a result has ten electrons surrounding it.
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