Problem 11 - Chemistry An Atoms First Approach

Question

In the hybrid orbital model, compare and contrast \(\sigma\) bonds with \(\pi\) bonds. What orbitals form the \(\sigma\) bonds and what orbitals form the \(\pi\) bonds? Assume the \(z\) -axis is the internuclear axis.

Step-by-Step Solution

Answer

In the hybrid orbital model, \(\sigma\) bonds are formed by the head-on overlap of orbitals (s-s, s-p, and p-p) along the internuclear axis and are stronger, allowing bond rotation. In contrast, \(\pi\) bonds result from side-by-side overlap of p orbitals perpendicular to the internuclear axis and are weaker, restricting bond rotation. \(\sigma\) bonds can be formed by various overlaps, while \(\pi\) bonds require p-p overlaps and always form in addition to a \(\sigma\) bond.

Step 1: Introduction

In the hybrid orbital model, chemical bonds are formed by the overlap of atomic orbitals which results in new hybrid orbitals. There are two types of covalent bonds: \(\sigma\) (sigma) bonds and \(\pi\) (pi) bonds. Let's compare and contrast these two types of bonds and identify the orbitals involved in their formation.

Step 2: Sigma (\(\sigma\)) Bonds

\(\sigma\) bonds are formed by the head-on or end-to-end overlap of atomic orbitals along the internuclear axis, which is the line connecting the nuclei of the two bonded atoms. They have a symmetrical distribution of electron density around the bond axis and can rotate freely. Due to this, they are the strongest type of covalent bond. The orbitals that can form \(\sigma\) bonds are the following: 1. A combination of two s orbitals (s-s overlap) 2. A combination of an s orbital and a p orbital (s-p overlap) along the internuclear axis 3. A combination of two p orbitals (p-p overlap) along the internuclear axis

Step 3: Pi (\(\pi\)) Bonds

\(\pi\) bonds are formed by the side-by-side overlap of atomic orbitals, with the electron density occurring above and below the internuclear axis. These bonds are weaker than \(\sigma\) bonds due to the less effective overlap of the orbitals. They occur in addition to a \(\sigma\) bond, typically as part of a double or triple bond, and restrict bond rotation due to the alignment of the overlapping orbitals. The orbitals that can form \(\pi\) bonds are the following: 1. A combination of two p orbitals (p-p overlap) perpendicular to the internuclear axis

Step 4: Comparison and Conclusion

To summarize, \(\sigma\) bonds and \(\pi\) bonds can be compared and contrasted as follows: 1. \(\sigma\) bonds are formed by head-on overlap of orbitals, while \(\pi\) bonds are formed by side-by-side overlap. 2. \(\sigma\) bonds are stronger and allow bond rotation, whereas \(\pi\) bonds are weaker and restrict bond rotation. 3. \(\sigma\) bonds can be formed by s-s, s-p, and p-p overlaps along the internuclear axis, whereas \(\pi\) bonds can be formed only by p-p overlaps perpendicular to the internuclear axis, and always in addition to a \(\sigma\) bond.