Multiple Choice
In which of the following compounds is the central atom's octet expanded to include 12 electrons?
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11. Bonding & Molecular Structure
Octet Rule
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Which of the following molecules contains an atom with an expanded octet?
A
CH4
B
NH3
C
SF6
D
CO2
Verified step by step guidance1
Recall that an expanded octet occurs when an atom has more than 8 electrons in its valence shell, which is possible for elements in period 3 or beyond because they have d orbitals available for bonding.
Examine each molecule and identify the central atom: CH4 has carbon (period 2), NH3 has nitrogen (period 2), SF6 has sulfur (period 3), and CO2 has carbon (period 2).
Determine the number of valence electrons around the central atom in each molecule by drawing or considering their Lewis structures.
Note that CH4, NH3, and CO2 all have central atoms that follow the octet rule strictly (8 electrons or fewer), while SF6 has sulfur bonded to six fluorine atoms, resulting in 12 electrons around sulfur, which is an expanded octet.
Conclude that SF6 contains an atom with an expanded octet because sulfur can accommodate more than 8 electrons due to its position in period 3, unlike the other molecules listed.
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