Which of the following statements correctly describes the Lewis structure and resonance of HCN (hydrogen cyanide)?

• A. HCN has resonance structures due to lone pairs on the hydrogen atom.
• B. HCN has two equivalent resonance structures involving the hydrogen atom.
• C. HCN exhibits resonance because the triple bond between C and N can be delocalized.
• D. HCN has a single valid Lewis structure with no resonance forms.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the Lewis structure of HCN by counting the total valence electrons. Hydrogen (H) has 1 valence electron, carbon (C) has 4, and nitrogen (N) has 5, giving a total of 10 valence electrons.
2. Step 2: Draw the skeletal structure with hydrogen bonded to carbon, and carbon bonded to nitrogen. Hydrogen can only form one bond, so it will be at one end.
3. Step 3: Arrange the electrons to satisfy the octet rule for carbon and nitrogen. Typically, carbon and nitrogen form a triple bond in HCN, with a single bond between hydrogen and carbon.
4. Step 4: Check for possible resonance structures by looking for alternative placements of electrons that maintain valid octets and overall charge. In HCN, the triple bond between carbon and nitrogen is localized and cannot be delocalized without breaking octet rules.
5. Step 5: Conclude that HCN has a single valid Lewis structure with no resonance forms because there are no alternative electron arrangements that satisfy the octet rule and maintain the molecule's stability.