Which is the correct Lewis electron dot structure for hydrogen cyanide, HCN? HCN HCN HCN:: HC:N: H:C:N
The Correct Answer and Explanation is:
The correct Lewis electron dot structure for hydrogen cyanide (HCN) is:
H–C≡N: or more fully shown as H:C≡N:
Explanation
Hydrogen cyanide (HCN) is a linear molecule composed of three atoms: hydrogen (H), carbon (C), and nitrogen (N). To determine its correct Lewis structure, we follow a step-by-step approach using the rules of chemical bonding and valence electrons.
Step 1: Count total valence electrons.
- Hydrogen has 1 valence electron.
- Carbon has 4 valence electrons.
- Nitrogen has 5 valence electrons.
Total = 1 + 4 + 5 = 10 valence electrons
Step 2: Determine the central atom.
Carbon is less electronegative than nitrogen and can form multiple bonds. So, carbon will be in the center, with hydrogen on one side and nitrogen on the other.
Basic skeleton: H – C – N
Step 3: Form bonds and satisfy octets.
- Start by placing single bonds between atoms: H–C–N uses up 2 bonds or 4 electrons.
- Remaining electrons: 10 – 4 = 6 electrons
To satisfy the octet rule, nitrogen needs 8 electrons, and carbon also needs 8. Hydrogen only needs 2, and it already has them from the single bond with carbon.
To complete the octets, we add multiple bonds between C and N. A triple bond between C and N satisfies the octet rule:
- Carbon: 2 electrons from H–C and 6 from C≡N = 8 total
- Nitrogen: 6 electrons from C≡N and 2 lone electrons = 8 total
The final structure: H–C≡N:
- Hydrogen has one bond (2 electrons) — complete
- Carbon has 4 bonds (8 electrons) — complete
- Nitrogen has 3 bonds and 1 lone pair (8 electrons) — complete
This arrangement uses all 10 electrons correctly and satisfies the octet rule for all atoms (except hydrogen, which follows the duet rule).
Therefore, the correct Lewis dot structure is H:C≡N:
