Sigma and pi-bonds

Introduction

In chemistry, understanding chemical bonding is crucial. When atoms interact, a bond holds them together. Chemical bonds are further divided into four types: ionic, covalent, polar, and hydrogen bonds. However, we’ll be talking about sigma bonds and pi bonds, which are both types of covalent bonds.

A sigma bond is a chemical link formed when the atomic orbitals of two atoms overlap linearly or co-axially. The electrons on the top and bottom of the axis linking the nuclei of the linked atoms form a pi bond, which is a sort of covalent bond. It’s made up of overlapping atomic orbitals in a parallel or lateral configuration. The chemical bonds between sigma and pi are covalent. The atomic orbital overlap creates sigma and pi bonds. Sigma bonds are created when two atomic orbital lobes overlap, whereas pi bonds are generated when one atomic orbital lobe overlaps another. A sigma bond has the same orbital structure as the p orbital, and a pi bond has the same orbital structure as the p orbital (again, as viewed along the bond axis, both times).

Sigma bonds are generally stronger than pi bonds. Both are widely utilized in molecular orbital theory to predict molecule behavior. Let’s understand sigma and pi bonds, types of sigma bonds, and the difference between sigma bond and pi bond.

The sigma bond(σ)

This type of covalent bond is formed by the overlap (same phase) of atomic orbitals along the internuclear axis. Due to the direct overlapping of the participating orbitals, sigma bonds are the strongest covalent bonds. An electron is an element that participates in a bond. A single bond is generally referred to as a sigma bond. 

Overlapping S-S

One orbital from each participating atom undergoes head-on overlapping along the internuclear axis in this type of overlapping. Before one s orbital can overlap with another, it must be half-filled. In H2 molecules, where each hydrogen atom has a half-filled s orbital, this form of overlap occurs.

Overlapping S-P

Along the internuclear axis, one half-filled s orbital overlaps with one half-filled p orbital, establishing a covalent connection.

In ammonia, this form of overlapping can be seen. The overlap of the 2px, 2py, and 2pz orbitals of the nitrogen atom with the 1s orbitals of the three hydrogen atoms forms three sigma bonds in an NH3 molecule.

Overlapping P-P

One half-filled p orbital from each participating atom overlaps head-on along the internuclear axis in this scenario. The 3pz orbitals of two chlorine atoms overlap p-p in a Cl2 molecule. It’s vital to remember that overlapping two p orbitals head-to-head forms a sigma bond, but overlapping the same orbitals laterally forms pi bonds.

The pi (π) bond

Pi bonds are formed when successive positive or same phase overlaps of atomic orbitals are perpendicular to the internuclear axis. The axis of the atomic orbitals are parallel to one another during bond formation, whereas the overlapping is perpendicular to the internuclear axis. Due to the substantially smaller degree of overlapping, pi bonds are often weaker than sigma bonds. A typical triple bond is made up of two pi bonds and one sigma bond, whereas a typical double bond is made up of one sigma bond and one pi bond. An individual sigma bond is generally weaker than a sigma and pi bond combination.

Difference between sigma bond and pi bond

Sigma bond

• Overlapping orbitals during the formation of a sigma bond can be one pure orbital and one hybrid orbital, or two pure orbitals and two hybrid orbitals.
• The sigma bonds can rotate freely and exist on their own.
• Bonds with a sigma value are more powerful.
• Sigma bonds are formed when atoms make contact.
• Only one sigma bond is created when two atoms are bonded together.
• Around the bond’s axis, sigma bonds are known to have cylindrical charge symmetry.
• Sigma bonds make atoms less reactive.
• The Sigma bond can be used to identify the shape of molecules.

Pi bond

• During the development of a pi bond, the overlapping orbitals must be two unhybridized orbitals.
• Pi-bonds must always exist in addition to the sigma bond, and rotation is limited.
• Typically, pi bonds are weaker than sigma bonds.
• It occurs after the formation of sigma bonds between two atoms that pi bonds are formed.
• Between two atoms, two pi bonds can occur.
• In pi bonds, there is no symmetry.
• When compared to atoms with simple sigma bonds, those having pi bonds are much more reactive.
• The pi bond cannot be used for the same purpose as the sigma bond.

Conclusion

In this article, we understood sigma bonds and pi-bonds, types of sigma bonds, the difference between sigma bonds & pi Bonds. A sigma bond is a chemical link formed when the atomic orbitals of two atoms overlap linearly or co-axially. The first bonds to form within molecules will be sigma bonds, which will be followed by pi bonds. Pi bonds are made up of atomic orbitals that are perpendicular to those that create sigma bonds.