Which statement is true about the formal charges in the cyanide ion (CN-)? Both carbon and nitrogen have zero formal charges. The carbon has a formal charge of -1. The nitrogen has a formal charge of +1. Both carbon and nitrogen have formal charges of +1.
The Correct Answer and Explanation is:
The correct answer is The carbon has a formal charge of -1.
Here’s the explanation:
The cyanide ion (CN-) consists of a carbon atom bonded to a nitrogen atom with a single negative charge distributed across the entire ion. To determine the formal charge of each atom in cyanide, we use the following formula for calculating formal charge:Formal Charge=Valence electrons of atom−(Nonbonding electrons+Bonding electrons2)\text{Formal Charge} = \text{Valence electrons of atom} – \left( \text{Nonbonding electrons} + \frac{\text{Bonding electrons}}{2} \right)Formal Charge=Valence electrons of atom−(Nonbonding electrons+2Bonding electrons)
- Carbon (C):
- Carbon is in group 14 of the periodic table, so it has 4 valence electrons.
- In the cyanide ion, carbon has a single bond with nitrogen and is also carrying one lone pair of electrons.
- Since the carbon-nitrogen bond is a single bond, it has 2 electrons shared between the two atoms. The lone pair of carbon adds 2 nonbonding electrons.
- So, the formal charge on carbon is calculated as follows: Formal charge of C=4−(2+22)=4−3=−1\text{Formal charge of C} = 4 – (2 + \frac{2}{2}) = 4 – 3 = -1Formal charge of C=4−(2+22)=4−3=−1 Thus, carbon has a formal charge of -1.
- Nitrogen (N):
- Nitrogen is in group 15, so it has 5 valence electrons.
- In cyanide, nitrogen is bonded to carbon and also has one lone pair of electrons. Nitrogen is sharing 2 electrons with carbon in a single bond, and its lone pair contributes 2 nonbonding electrons.
- The formal charge on nitrogen is calculated as: Formal charge of N=5−(2+22)=5−3=+1\text{Formal charge of N} = 5 – (2 + \frac{2}{2}) = 5 – 3 = +1Formal charge of N=5−(2+22)=5−3=+1 Therefore, nitrogen has a formal charge of +1.
In the cyanide ion, the negative charge is mainly located on the carbon atom, while nitrogen carries a positive formal charge. The total charge of the ion is -1, as indicated by the overall formal charges of the atoms.
