In the molecule HCN, which atom is most likely to bear a formal charge in its most stable Lewis structure?

• A. Carbon (C)
• B. Nitrogen (N)
• C. None of the atoms bear a formal charge
• D. Hydrogen (H)

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the concept of formal charge, which helps determine the distribution of electrons in a Lewis structure. The formal charge (FC) on an atom is calculated using the formula: \(\text{FC} = V - (L + \frac{B}{2})\), where \(V\) is the number of valence electrons in the free atom, \(L\) is the number of lone pair electrons on the atom in the molecule, and \(B\) is the number of bonding electrons shared with other atoms.
2. Step 2: Draw the Lewis structure of HCN. Hydrogen (H) is bonded to Carbon (C), which is triple bonded to Nitrogen (N). Assign lone pairs to nitrogen to complete its octet, and check that hydrogen has only 2 electrons (duet rule).
3. Step 3: Count the valence electrons for each atom: H has 1, C has 4, and N has 5 valence electrons. Then, count the lone pair electrons and bonding electrons around each atom in the Lewis structure.
4. Step 4: Calculate the formal charge for each atom using the formula from Step 1. For example, for carbon, count its valence electrons, lone pairs, and bonding electrons, then apply the formula. Repeat for nitrogen and hydrogen.
5. Step 5: Analyze the formal charges calculated. The most stable Lewis structure usually has formal charges closest to zero on all atoms. If all atoms have a formal charge of zero, then none of the atoms bear a formal charge in the most stable Lewis structure.