Multiple Choice
Which of the following compounds is an exception to the octet rule?
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11. Bonding & Molecular Structure
Lewis Dot Structures: Exceptions
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Which of the following molecules can have an expanded octet in their Lewis dot structure?
A
CH4
B
CO2
C
NH3
D
SF6
Verified step by step guidance1
Recall that an expanded octet occurs when a central 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.
Identify the central atom in each molecule and determine its period in the periodic table: CH4 (C, period 2), CO2 (C, period 2), NH3 (N, period 2), SF6 (S, period 3).
Since carbon (C) and nitrogen (N) are in period 2, they cannot have expanded octets because they lack accessible d orbitals; thus, CH4, CO2, and NH3 cannot have expanded octets.
Sulfur (S) is in period 3, so it can utilize d orbitals to accommodate more than 8 electrons, allowing SF6 to have an expanded octet.
Therefore, only SF6 can have an expanded octet in its Lewis dot structure.
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