Below is the Lewis structure of the hydrogen cyanide (HCN) molecule. H:C:: N: Count the number of bonding pairs and the number of lone pairs around the carbon atom in this molecule. bonding pairs: lone pairs: None
The correct answer and explanation is:
Correct Answer:
- Bonding pairs around the carbon atom: 4
- Lone pairs around the carbon atom: 0
Explanation:
The Lewis structure for hydrogen cyanide (HCN) is written as:
H : C ≡ N :
Here’s how the structure and pair counts are determined:
- Bonding pairs:
- Carbon forms a single bond with hydrogen (H).
- Carbon forms a triple bond with nitrogen (N).
- A single bond corresponds to 1 bonding pair (2 electrons), and a triple bond corresponds to 3 bonding pairs (6 electrons).
- Total bonding pairs around the carbon atom = 1 (from H-C) + 3 (from C≡N) = 4 bonding pairs.
- Lone pairs:
- Carbon contributes 4 valence electrons, and all 4 are involved in bonding. Therefore, there are no lone pairs on the carbon atom.
- Context for the molecule:
- Hydrogen has 1 valence electron, and it forms a single bond with carbon, satisfying its octet.
- Nitrogen has 5 valence electrons, and in this structure:
- It forms a triple bond with carbon (uses 3 electrons for bonding).
- It has 1 lone pair of electrons left (2 non-bonded electrons).
- The overall structure satisfies the octet rule for all atoms.
- Why the carbon has no lone pairs:
- Carbon has exactly 4 valence electrons. It achieves a stable configuration by sharing these electrons through bonding (1 with hydrogen and 3 with nitrogen). Since all its valence electrons are used in bonds, no lone pairs remain on the carbon atom.
Thus, carbon in HCN has 4 bonding pairs and 0 lone pairs, making it a linear molecule.