What is the molecular geometry of the OCN- (cyanate) ion?

• A. Linear
• B. Tetrahedral
• C. Trigonal planar
• D. Bent

Answer: (A)

Verified step by step guidance

1. Step 1: Determine the Lewis structure of the OCN⁻ ion by counting the total number of valence electrons. Oxygen has 6, carbon has 4, nitrogen has 5, and there is an extra electron due to the negative charge, so total electrons = 6 + 4 + 5 + 1 = 16 electrons.
2. Step 2: Arrange the atoms with carbon in the center (since it is less electronegative than oxygen and nitrogen) and connect oxygen and nitrogen to carbon with single bonds initially.
3. Step 3: Distribute the remaining electrons to satisfy the octet rule for each atom, forming double or triple bonds as necessary to minimize formal charges and achieve the most stable Lewis structure.
4. Step 4: Count the regions of electron density (bonding and lone pairs) around the central atom (carbon). For OCN⁻, carbon is bonded to two atoms and has no lone pairs, so there are two regions of electron density.
5. Step 5: Use the VSEPR theory to determine the molecular geometry based on the number of electron density regions. Two regions of electron density around the central atom correspond to a linear geometry.