MCAT General Chemistry Question 40: Answer and Explanation

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Question: 40

10. Although the octet rule dictates much of molecular structure, some atoms can violate the octet rule by being surrounded by more than eight electrons. Which of the following is the best explanation for why some atoms can exceed the octet?

  • A. Atoms that exceed the octet already have eight electrons in their outermost electron shell.
  • B. Atoms that exceed the octet only do so when bonding with transition metals.
  • C. Atoms that exceed the octet can do so because they have d-orbitals in which extra electrons can reside.
  • D. Some atoms can exceed the octet because they are highly electronegative.

Correct Answer: C

Explanation:

All atoms in the third period or greater have d-orbitals, which can hold an additional 10 electrons. The typical "octet" electrons reside in s- and p-orbitals, but elements in period 3 or higher can place electrons into these d-orbitals.

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