Lewis Structure :N-C-C-N: Total # O Sigma Bonds Total # of Pi Bonds
The Correct Answer and Explanation is:
Total # of Sigma Bonds: 3
Total # of Pi Bonds: 4
Explanation
To determine the number of sigma (σ) and pi (π) bonds in the Lewis structure for dicyanogen, :N≡C−C≡N:, we must first understand the composition of single, double, and triple covalent bonds.
Sigma (σ) Bonds: A sigma bond is the first covalent bond formed between two atoms. It is created by the direct, head-on overlap of atomic orbitals along the imaginary line connecting the two nuclei. Every covalent bond, regardless of whether it is single, double, or triple, contains exactly one sigma bond. These bonds are the strongest type of covalent bond.
Pi (π) Bonds: Pi bonds are formed by the parallel, or sideways, overlap of p-orbitals. They can only form after a sigma bond has already been established between two atoms. Pi bonds constitute the second bond in a double bond and the second and third bonds in a triple bond. They are generally weaker than sigma bonds.
The rules are as follows:
- A single bond consists of 1 sigma bond.
- A double bond consists of 1 sigma bond and 1 pi bond.
- A triple bond consists of 1 sigma bond and 2 pi bonds.
Now, let’s analyze the molecule :N≡C−C≡N: step by step:
- Central C−C Bond: There is a single bond connecting the two carbon atoms. According to our rules, this single bond consists of 1 sigma bond.
- Two N≡C Bonds: The molecule has two identical triple bonds, one between each nitrogen and carbon atom. Each triple bond is composed of 1 sigma bond and 2 pi bonds.
To find the total number of each type of bond, we sum the counts from each part of the molecule:
- Total Sigma (σ) Bonds: We add the sigma bond from the central C−C bond and one sigma bond from each of the two N≡C triple bonds.
Total σ = 1 (from C−C) + 1 (from N≡C) + 1 (from C≡N) = 3 sigma bonds. - Total Pi (π) Bonds: We add the pi bonds from the two N≡C triple bonds. The central C−C single bond contributes no pi bonds.
Total π = 2 (from the first N≡C) + 2 (from the second C≡N) = 4 pi bonds.
Therefore, the dicyanogen molecule contains a total of 3 sigma bonds and 4 pi bonds. The lone pairs on the nitrogen atoms are non-bonding electrons and do not contribute to this count
