Which of the following molecules contains an atom that does not obey the octet rule?

• A. CH4
• B. CO2
• C. NH3
• D. BF3

Answer: (D)

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 stable electron configuration similar to noble gases.
2. Examine each molecule to determine if all atoms obey the octet rule by counting the valence electrons around each atom after bonding:
3. For CH4 (methane), carbon forms four single bonds with hydrogen, giving carbon 8 electrons in its valence shell, so it obeys the octet rule.
4. For CO2 (carbon dioxide), carbon forms two double bonds with oxygen atoms, resulting in 8 electrons around carbon and oxygen atoms, so all obey the octet rule.
5. For NH3 (ammonia), nitrogen forms three single bonds with hydrogen and has one lone pair, totaling 8 electrons around nitrogen, so it obeys the octet rule.
6. For BF3 (boron trifluoride), boron forms three single bonds with fluorine atoms but only has 6 electrons around it, which means boron does not obey the octet rule and is electron-deficient.