Question 8.4.1: Use the formal charge for each atom in the cyanide ion, CN^−......
Use the formal charge for each atom in the cyanide ion, CN^{−}, to predict whether H^{+} is more likely to attach to carbon or nitrogen when forming hydrocyanic acid.
You are asked to identify the formal charge for every atom in a polyatomic ion and to use formal charge to predict the attachment site of H^{+}.
You are given the chemical formula for the polyatomic ion.
First draw the Lewis structure of CN^{-}.
Use Equation 8.3 to calculate the formal charge for carbon and nitrogen.
C formal charge = (4) − [2 + ½(6)] = −1
N formal charge = (5) − [2 + ½(6)] = 0
When the positively charged H^{+} ion attaches to CN^{-}, it is more likely to attach to the atom with the negative formal charge, forming H-C≡N.
Is your answer reasonable? Notice that the sum of the formal charges is equal to the overall charge on the ion (−1).