Which molecule below has a Lewis structure that is an exception to the octet rule?

• A. CO2
• B. NH3
• C. BF3
• D. CH4

Answer: (C)

Verified step by step guidance

1. Recall that the octet rule states atoms tend to form bonds until they are surrounded by eight electrons in their valence shell, achieving a noble gas configuration.
2. Examine the Lewis structures of each molecule: CO2, NH3, BF3, and CH4, by counting the total valence electrons and distributing them to satisfy the octet rule for each atom.
3. For CO2, carbon forms double bonds with each oxygen, satisfying the octet rule for all atoms.
4. For NH3 and CH4, nitrogen and carbon form single bonds with hydrogen atoms, also satisfying the octet rule.
5. For BF3, boron forms three single bonds with fluorine atoms but only has six electrons around it, making it an exception to the octet rule because boron is stable with less than eight electrons.