Using Lewis structures and formal charge, which of the following ions is most stable? OCN⁻ ONC⁻ NOC⁻

Question

Quizplus · Accepted Answer

To determine the most stable ion, we need to draw the Lewis structures and calculate the formal charges.

OCN⁻:

O = 6 valence electrons 
C = 4 valence electrons 
N = 5 valence electrons 
One extra electron for the ion

Total valence electrons = 16

To form the structure, C will be the central atom, and O and N will be bonded to it. The structure will have a triple bond between the C and N atoms, and a single bond between the N and O atoms.

From the Lewis structure, we can calculate the formal charges:

Formal charge of O = 6 - 6 - 1/2(4) = -1 
Formal charge of C = 4 - 0 - 1/2(6) = 0 
Formal charge of N = 5 - 4 - 1/2(6) = -1

The total formal charge of the ion = -1

ONC⁻:

The Lewis structure will be the same as OCN⁻, but the positions of the atoms will be different.

From the Lewis structure, we can calculate the formal charges:

Formal charge of O = 6 - 6 - 1/2(2) = 0 
Formal charge of N = 5 - 4 - 1/2(8) = -1 
Formal charge of C = 4 - 0 - 1/2(2) = 0

The total formal charge of the ion = -1

NOC⁻:

The Lewis structure will have a double bond between N and O and a single bond between C and N.

From the Lewis structure, we can calculate the formal charges:

Formal charge of N = 5 - 4 - 1/2(4) = 0 
Formal charge of O = 6 - 6 - 1/2(6) = -1 
Formal charge of C = 4 - 0 - 1/2(8) = +1

The total formal charge of the ion = 0

Based on the formal charges, OCN⁻ is the most stable ion because the formal charges are evenly distributed, and the total formal charge is negative, indicating the ion is more stable than the neutral molecule. In contrast, ONC⁻ has an atom (O) with a formal charge of 0, which indicates there is no charge separation and the ion is less stable. Also, NOC⁻ has a formal charge of +1 on C, indicating that the ion is unstable. Therefore, the best choice for the most stable ion is A, OCN⁻.

Using Lewis Structures and Formal Charge, Which of the Following