Final answer:
The formal charge is the hypothetical charge an atom in a molecule or ion would have if the bonding electrons were shared equally between atoms. To calculate the formal charge of an atom, you subtract the number of valence electrons of a free atom from the number of lone pair electrons and half the number of bonding electrons around the atom. In the case of the thiocyanate ion (SCN-), the best Lewis structure is SCN- with a formal charge of 0 on each atom.
Step-by-step explanation:
The formal charge is the hypothetical charge an atom in a molecule or ion would have if the bonding electrons were shared equally between atoms.
To calculate the formal charge of an atom, you subtract the number of valence electrons of a free atom from the number of lone pair electrons and half the number of bonding electrons around the atom.
For example, in the thiocyanate ion (SCN-), there are three possible Lewis structures: SCN-, CNS, and CSN. To determine the best structure, we assign formal charges to each atom in each structure. In the SCN- structure, the formal charges for each atom are as follows: S = 1, C = 2, and N = 0. Therefore, the best Lewis structure for SCN- would be SCN- with a formal charge of 0 on each atom.