After drawing the Lewis structure of HCN, what are the electron domain geometry and molecular geometry around the central carbon atom?

• A. Electron domain geometry: tetrahedral; Molecular geometry: trigonal pyramidal
• B. Electron domain geometry: trigonal planar; Molecular geometry: linear
• C. Electron domain geometry: trigonal planar; Molecular geometry: bent
• D. Electron domain geometry: linear; Molecular geometry: linear

Answer: (D)

Verified step by step guidance

1. Step 1: Draw the Lewis structure of HCN. Carbon (C) is the central atom bonded to hydrogen (H) on one side and nitrogen (N) on the other. Carbon forms a single bond with hydrogen and a triple bond with nitrogen.
2. Step 2: Count the regions of electron density (electron domains) around the central carbon atom. Each bond (single, double, or triple) counts as one electron domain. Here, carbon has two electron domains: one single bond to H and one triple bond to N.
3. Step 3: Determine the electron domain geometry based on the number of electron domains around the central atom. Two electron domains correspond to a linear electron domain geometry.
4. Step 4: Determine the molecular geometry by considering the positions of atoms only (ignoring lone pairs). Since there are no lone pairs on carbon and two bonded atoms, the molecular geometry is also linear.
5. Step 5: Conclude that both the electron domain geometry and molecular geometry around the central carbon atom in HCN are linear.