**Part B.** Two possible electron-dot structures are shown for the cyanate ion, NCO^{−} . What can you conclude about how favorable the structures are?

a. Structure A is more favored

b. Structure B is more favored

c. The structure are equally favored

Formal charge (FC) keeps track of which electrons an atom "owns" in a chemical bond with the equation

$\mathbf{FC}\mathbf{}\mathbf{=}(\mathrm{valence}{e}^{-}\mathrm{in}\mathrm{free}\mathrm{atom})\mathbf{}\mathbf{-}\mathbf{}(\mathrm{valence}{e}^{-}\mathrm{in}\mathrm{bonded}\mathrm{atom})$

When more than one valid Lewis structure can be drawn for a particular molecule, formal charge is used to predict the most favorable structure.

A bonded atom is considered to "own" all its nonbonding electrons but only half of the bonding electrons because these are shared with another atom. Therefore, the formal charge formula can be rewritten as follows:

$\mathbf{FC}\mathbf{}\mathbf{=}\mathbf{(}\mathbf{valence}\mathbf{}{\mathbf{e}}^{\mathbf{-}}\mathbf{}\mathbf{in}\mathbf{}\mathbf{free}\mathbf{}\mathbf{atom}\mathbf{)}\mathbf{}\mathbf{-}\mathbf{}[\left(\mathrm{nonbonding}{e}^{-}\mathrm{shown}\right)+\frac{1}{2}\left(\mathrm{bonding}{e}^{-}\mathrm{shown}\right)]$

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What scientific concept do you need to know in order to solve this problem?

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