Question

resonance structures and formal charges
go back to the resonance structures you drew for scn-, n2o and ocs. assign formal charges to all the atoms in each resonance structure and then determine which resonance structure is the dominant resonance structure.

Explanation:

Step1: Draw resonance structures for SCN⁻

SCN⁻ has three main resonance - structures. In one structure, the triple bond is between C and N, and S has a formal charge of - 1. In another, the triple bond is between C and S, and N has a formal charge of - 1. The third has a double - bond between each atom with formal charges on S and N. The most stable (dominant) resonance structure has the negative formal charge on the more electronegative atom (N).

Step2: Draw resonance structures for N₂O

N₂O has three resonance structures. One has a triple bond between the two N atoms and a single bond between N and O. Another has a double - bond between each atom. The third has a triple bond between N and O and a single bond between the two N atoms. The dominant resonance structure has the negative formal charge on the more electronegative atom (O).

Step3: Draw resonance structures for OCS

OCS has three resonance structures. One has a triple bond between C and S and a single bond between C and O. Another has a triple bond between C and O and a single bond between C and S. The third has double - bonds between each atom. The dominant resonance structure has the negative formal charge on the more electronegative atom (O).

Answer:

For SCN⁻: The dominant resonance structure has a triple bond between C and N and a single bond between C and S, with a formal charge of - 1 on N.
For N₂O: The dominant resonance structure has a double - bond between the two N atoms and a double - bond between N and O, with a formal charge of - 1 on O.
For OCS: The dominant resonance structure has double - bonds between C=O and C=S, with a formal charge of - 1 on O.