Question

How many pi bonds and sigma bonds are there in the tetracyanoethylene molecule?

Short answer

There are 9 pi bonds and 7 sigma bonds present in a tetracyanoethylene molecule.

Step-by-step solution

Understand the Molecule

Tetracyanoethylene is a molecule with the formula (C2N2)2. It consists of two carbon (C) atoms in the center and four cyano groups (CN) attached to the carbon atoms. Each cyano group consists of 1 carbon atom and 1 nitrogen atom (N). Thus overall, the molecule has four Carbon atoms and four Nitrogen atoms.

Analyze the molecule

Carbon in the cyano group forms a triple bond with the Nitrogen atom. In a triple bond, one bond is a sigma bond, and the other two are pi bonds. Furthermore, the central carbon atoms form a double bond. A double bond consists of one sigma bond and one pi bond.

Calculations

There are four instances of a triple bond in the molecule (each of them in a CN group). Hence, the number of pi bonds in the molecule is 4*2 = 8. Moreover, the double bond in the center contributes one more pi bond, thus the total pi bonds would be 8 + 1 = 9. As for sigma bonds, there are four instances of a triple bond, contributing 4 sigma bonds and the double bond in the center contributes one more sigma bond. The connection between the two central carbon atoms and the neighboring carbon atoms of the cyano groups gives additional 2 sigma bonds. Hence the total number of sigma bonds is 4 + 1 + 2 = 7.