Formal charge (FC) keeps track of which electrons an atom \"owns\" in a chemical

Question

Formal charge (FC) keeps track of which electrons an atom "owns" in a chemical bond with the equation FC = (valence e^- in free atom - (valence e^- in bonded 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: FC = (valence e^- in free atom) -1/2 (bonding e^- shown) - (nonbonding e^- shown) For a molecule of fluorous acid, the atoms are arranged as HOFO. What is the formal charge on each of the atoms? Enter the formal charges in the same order as the atoms are listed. Express your answers as charges separated by comma. For example, a positive one charge would be written as Two possible electron-dot structures are shown for the cyanate ion. NCO^-. What can you conclude about how favorable the structures are?

Explanation / Answer

Formal charge = Valence electrons - Bonding electrons - Nonbonding electrons

Formal charge of H = 1-1-0 = 0

Formal charge of O = 6-2-4= 0

Formal charge of F = 7-2-4 = +1

Formal charge of O = 6-1-6 = -1

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Part B :

Nitrogen is less electonegative than Oxygen atom. It is more likely to give up electrons tothe more electronegative species. So, the negative charge is on the O atom. There aren't enough valence electrons to obtain an octet without sharing. Therefore, there exists a triple bond between Nitrogen and Carbon atom.

There exists a triple bond between C and N in resonance structure A. Therefore, structure A is more favored.

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