CHEMISTRY · Multi-part · AP · Chemistry · Compound Structure and Properties · Compound Structure and Properties
Problem
The thiocyanate ion, SCN⁻, is a pseudohalide that forms complexes with many transition metals. Two nonequivalent Lewis diagrams are proposed below.
• Structure X: S double-bonded to C and C triple-bonded to N. Lone pairs are added so that each atom appears to have an octet.
• Structure Y: S single-bonded to C, C triple-bonded to N, and the negative charge localized on sulfur. Lone pairs are added so that each atom appears to have an octet.
Respond to the tasks that follow.
(a) Calculate the formal charge on each atom in Structure X.
(b) Calculate the formal charge on each atom in Structure Y.
(c) Using the results from parts (a) and (b) and electronegativity trends within the periodic table, determine which structure is more plausible for SCN⁻. Provide a clear justification.
(d) Draw a resonance hybrid that summarizes the bonding in SCN⁻, clearly indicating the locations of any partial charges and illustrating the relative contributions of Structures X and Y.