Final answer:
The polyatomic ion thiocyanate has the formula SCN-, which includes one sulfur, one carbon, and one nitrogen atom. The SCN- structure is favored by formal charge distribution. When writing formulas with multiple thiocyanate ions in a compound, parentheses are used around SCN with a subscript indicating quantity.
Step-by-step explanation:
The formula for the polyatomic ion thiocyanate is SCN−. Thiocyanate is a negative ion, or anion, consisting of one sulfur atom, one carbon atom, and one nitrogen atom. While thiocyanate can theoretically have different structures, such as NCS−, CNS−, or CSN−, the most common structure is SCN−. The arrangement of atoms in thiocyanate is influenced by the formal charges, and SCN− tends to be the most stable with respect to the formal charges on each atom.
In the construction of formulas for ionic compounds containing polyatomic ions like thiocyanate, it is crucial to ensure that the overall charges balance. If multiple thiocyanate ions are needed in a compound, the entire formula for the thiocyanate ion would be enclosed in parentheses with the appropriate numerical subscript outside the parentheses to indicate the number of these ions in the compound. For instance, if a compound contains two thiocyanate ions, it would be written as (SCN)2.