Which of the following compounds is an exception to the octet rule?

• A. ClF_3
• B. HCl
• C. CCl_4
• D. H_2O

Answer: (A)

Verified step by step guidance

1. Recall the octet rule, which states that 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 compound to determine if the central atom follows the octet rule: For HCl, chlorine is bonded to hydrogen and has three lone pairs, completing its octet.
3. For CCl_4, carbon forms four single bonds with chlorine atoms, resulting in eight electrons around carbon, satisfying the octet rule.
4. For H_2O, oxygen forms two single bonds with hydrogen atoms and has two lone pairs, giving oxygen a total of eight electrons, thus following the octet rule.
5. For ClF_3, chlorine is bonded to three fluorine atoms and also has two lone pairs, resulting in more than eight electrons around chlorine, making it an exception to the octet rule due to an expanded valence shell.