Question

How to figure out the amount of sigma and pi bonds?

a) Count the single bonds for sigma bonds and double bonds for pi bonds
b) Count the double bonds for sigma bonds and triple bonds for pi bonds
c) Count the single bonds for sigma bonds and double bonds for pi bonds
d) Count the triple bonds for sigma bonds and quadruple bonds for pi bonds

Answer 1

Count single bonds for sigma bonds and for pi bonds, consider one for each double bond and two for each triple bond. Write the Lewis structure, count regions of electron density for sigma bonds, and identify double or triple bonds for pi bonds.

Step-by-step explanation:

To determine the amount of sigma and pi bonds in a molecule, you can follow these general rules:

• Each single bond in a molecule is a sigma bond.
• Double bonds consist of one sigma bond and one pi bond.
• Triple bonds consist of one sigma bond and two pi bonds.

Therefore, the correct answer to the student's question is that you count single bonds for sigma bonds, and for pi bonds, you consider double bonds (one pi bond) and triple bonds (two pi bonds). This can be summarized as:

1. Write the Lewis structure of the molecule or polyatomic ion.
2. Count the number of regions of electron density (lone pairs and bonds) around the central atom; each region constitutes a sigma bond.
3. Additionally, identify the presence of double or triple bonds, adding a pi bond for each double bond and two pi bonds for each triple bond

For example, in a molecule of ethene (C₂H₄), which has a double bond between the carbon atoms, you would count a total of five sigma bonds (four C-H single bonds and one C-C single bond component of the double bond) and one pi bond (the second bond of the double bond).