How many lone pairs of electrons are found on the central atom of HCN

How many lone pairs of electrons are found on the central atom of HCN?

The Correct Answer and Explanation is:

Correct Answer:
Zero (0) lone pairs of electrons are found on the central atom of HCN.

Explanation:

HCN (hydrogen cyanide) is a linear molecule with the chemical formula H–C≡N. To determine the number of lone pairs on the central atom, we must first understand the Lewis structure and the electron configuration.

1. Identify the atoms involved:
   • H (hydrogen)
   • C (carbon)
   • N (nitrogen)
2. Determine the central atom:
   Carbon is the central atom because it can form four bonds and is more capable of acting as a bridge between hydrogen and nitrogen.
3. Count total valence electrons:
   • Hydrogen contributes 1 valence electron.
   • Carbon contributes 4 valence electrons.
   • Nitrogen contributes 5 valence electrons.
     Total = 1 + 4 + 5 = 10 valence electrons
4. Construct the basic skeleton:
   Arrange atoms as H–C–N.
5. Distribute electrons to satisfy the octet rule:
   • Hydrogen forms a single bond with carbon.
   • Carbon forms a triple bond with nitrogen to fulfill the octet for both atoms.
   • The triple bond accounts for 6 electrons between carbon and nitrogen.
   • One single bond connects hydrogen to carbon (2 electrons).
   • This uses 8 electrons in bonds.
   • The remaining 2 electrons go as a lone pair on nitrogen.
6. Check the central atom (carbon):
   • Carbon is involved in four bonds (1 single bond with H and 3 with N).
   • It uses all 4 of its valence electrons in bonding.
   • Therefore, carbon has no lone pairs.
7. Conclusion:
   The central atom (carbon) in HCN has zero lone pairs. All its valence electrons are involved in bonding, creating a linear geometry with no unshared pairs around carbon.