Question

a student proposes the following lewis structure for the isocyanate (nco^-) ion.
:c\equiv o - \ddot{n}: ^-
assign a formal charge to each atom in the students lewis structure.

Explanation:

Step1: Recall formal charge formula

Formal charge \(=\text{Valence electrons}-\text{Non - bonding electrons}-\frac{1}{2}\text{Bonding electrons}\)

Step2: Calculate for \(C\)

Valence electrons of \(C = 4\). Non - bonding electrons \(= 2\). Bonding electrons \(= 6\).
Formal charge \(=4 - 2-\frac{1}{2}\times6=4 - 2 - 3=-1\)

Step3: Calculate for \(O\)

Valence electrons of \(O = 6\). Non - bonding electrons \(= 0\). Bonding electrons \(= 6\).
Formal charge \(=6-0-\frac{1}{2}\times6=6 - 3=+3\)

Step4: Calculate for \(N\)

Valence electrons of \(N = 5\). Non - bonding electrons \(= 6\). Bonding electrons \(= 2\).
Formal charge \(=5 - 6-\frac{1}{2}\times2=5 - 6 - 1=-2\)

Answer:

atom	formal charge
\(O\)	\(+3\)
\(N\)	\(-2\)