Question

What are the formal charges on the sulfur (s), carbon (c), and nitrogen (n) atoms, respectively, in the resonance structure that contributes most to the stability of the thiocyanate ion, scn−?

Answer 1

Answer:

Sulfur: -1

Carbon: 0

Nitrogen: 0

Explanation:

The thiocyanate ion SCN- can have only two resonance structures, which are:

S - C ≡ N <--------> S = C = N

In the first structure, we have one single bond and one triple bond, in this case, the negative charge is located in the sulfur. This is because Sulfur have 6 electrons and those electrons are present in the atom, (see picture below), and counting the electron that is sharing with the Carbon, the total electrons that sulfur has is 7 (It has one more than usual). Carbon and nitrogen are already stable with 0 of formal charge, because carbon can only have 4 electrons which 1 is sharing with sulfur and the other 3 with the nitrogen, and nitrogen have 5 electrons, three sharing with carbon and the other two kept it for itself.

In the second structure, the negative charge of the sulfur is transfered to the nitrogen, meaning that it has 6 electrons the nitrogen (formal charge -1) and carbon and sulfur with 4 and 6 electrons respectively.

Between these two structures, the most stable is the first one basically because Sulfur is a better nucleophile than the Nitrogen, and can form stronger hydrogen bond in acid, giving more stable structure.

Answer 2

Answer:

0, 0, -1  

Explanation:

There are three resonance contributors to the resonance hybrid of the SCN⁻ ion.

The one on the right is the least stable because it has the greatest separation of charge.

The remaining structures each have one negative charge.

The structure in the middle is the most stable and most important contributor because it has the negative charge on the most electronegative atom —  N.

The formal charges on S, C, and N are 0, 0, and -1.