Which of the following molecules has a Lewis structure that is not consistent with the octet rule?

• A. CO2
• B. BF3
• C. NH3
• D. CH4

Answer: (B)

Verified step by step guidance

1. Recall the octet rule: atoms tend to form bonds until they are surrounded by eight electrons in their valence shell, achieving a noble gas configuration.
2. Draw the Lewis structure for each molecule to check if all atoms satisfy the octet rule:
3. For CO2, carbon forms two double bonds with oxygen atoms, giving carbon 8 electrons and each oxygen 8 electrons, satisfying the octet rule.
4. For NH3, nitrogen forms three single bonds with hydrogen atoms and has one lone pair, totaling 8 electrons around nitrogen, satisfying the octet rule.
5. For CH4, carbon forms four single bonds with hydrogen atoms, totaling 8 electrons around carbon, satisfying the octet rule.
6. For BF3, boron forms three single bonds with fluorine atoms but only has 6 electrons around it, which does not satisfy the octet rule, making BF3 the exception.