In the BEST Lewis Structure for the cyanate ion, CNO-, the formal charges on the atoms are as follows:
A. OC=+1, N=+1, O=+1
B C=0, N=0, O=-1
C C=0, N=-1, O=+1
D C=-1, N=-1, O=-1
E C=0, N=+1, O=+1
The correct answer and explanation is :
The correct answer is C: C=0, N=-1, O=+1.
Explanation:
To determine the formal charges on the atoms in the cyanate ion (CNO⁻), we need to follow these steps:
- Determine the Lewis Structure:
The cyanate ion consists of carbon (C), nitrogen (N), and oxygen (O), and has a negative charge, meaning there is one extra electron compared to the neutral molecule. This extra electron will influence the formal charge calculations. The correct Lewis structure has carbon (C) bonded to nitrogen (N), which is in turn bonded to oxygen (O). The ion is linear, and oxygen typically carries a negative charge in this structure. - Calculate the Formal Charges:
The formula for formal charge is: [
\text{Formal charge} = \text{Valence electrons} – (\text{Lone pair electrons} + \frac{1}{2} \times \text{Bonding electrons})
] Now, let’s break it down atom by atom:
- Carbon (C):
Carbon has 4 valence electrons. In the Lewis structure, it forms a single bond with nitrogen and a triple bond with oxygen. Carbon has no lone pairs. Therefore, the formal charge on carbon is: [
\text{Formal charge on C} = 4 – (0 + \frac{1}{2} \times 4) = 4 – 2 = 0
] - Nitrogen (N):
Nitrogen has 5 valence electrons. It forms a single bond with carbon and a triple bond with oxygen. Nitrogen also has one lone pair of electrons. Therefore, the formal charge on nitrogen is: [
\text{Formal charge on N} = 5 – (2 + \frac{1}{2} \times 6) = 5 – (2 + 3) = 5 – 5 = 0
] - Oxygen (O):
Oxygen has 6 valence electrons. It forms a triple bond with nitrogen and has two lone pairs of electrons. Therefore, the formal charge on oxygen is: [
\text{Formal charge on O} = 6 – (4 + \frac{1}{2} \times 6) = 6 – (4 + 3) = 6 – 7 = -1
]
- Final Formal Charges:
After calculating the formal charges for each atom, we get:
- Carbon: 0
- Nitrogen: -1
- Oxygen: +1
Thus, the correct choice is C: C=0, N=-1, O=+1, as it provides the correct distribution of formal charges on each atom in the cyanate ion, and the overall charge on the ion is -1, which is consistent with the negative charge on the molecule.