Textbook Question
(a) Which of these compounds is an exception to the octet rule: carbon dioxide, water, ammonia, phosphorus trifluoride, or arsenic pentafluoride?
11. Bonding & Molecular Structure
Octet Rule
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Which of the following contains an atom that may have an incomplete octet?
A
CCl4
B
NCl3
C
OCl2
D
SeCl6
E
BCl3
Verified step by step guidance1
Step 1: Understand the concept of the octet rule, which states that atoms tend to form compounds in ways that give them eight valence electrons, achieving a noble gas electron configuration.
Step 2: Identify the central atom in each compound. For CCl4, the central atom is carbon (C); for NCl3, it is nitrogen (N); for OCl2, it is oxygen (O); for SeCl6, it is selenium (Se); and for BCl3, it is boron (B).
Step 3: Recall that some elements, particularly those in the second period of the periodic table, such as boron, can have less than eight electrons in their valence shell and still be stable. This is known as an incomplete octet.
Step 4: Analyze each compound to determine if the central atom can have an incomplete octet. Boron in BCl3 is known to form stable compounds with only six valence electrons, making it an exception to the octet rule.
Step 5: Conclude that BCl3 is the compound where the central atom, boron, may have an incomplete octet, as it is stable with only six electrons in its valence shell.
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