Types of covalent bonds(sigma and pi)

Types of covalent bonds(sigma and pi)

Hello friends…. let’s start with the topic Types of covalent bonds(sigma and pi).

Types of covalent bonds(sigma and pi bond) atomic orbital convert into molecular orbital. Or we can say, the covalent bond is formed when the atomic orbitals having an unpaired electron combining atoms overlap together. (Types of covalent bonds(sigma and pi)

In covalent bonding, overlapping depends on the fact that which type of molecule is going to form and which type of covalent bonding is being done by it, which means either only sigma bonding (like saturated hydrocarbon methane, ethane, etc) or sigma and pi bonding (like unsaturated hydrocarbon ethylene, acetylene, etc). (Types of covalent bonds(sigma and pi)

Chemical bonding and its types

Important note- 

Whenever a covalent bonding occurs, the first bond is a sigma bond, then depending on the type of molecules, there would be the formation of another sigma or pi bond.

Or we can say that the sigma bond is a basic bond, we cannot imagine a covalent bond without a sigma bond.

Till now, you must have understood that covalent bonds are of two types, one is sigma and the second is pi bond. Now we are going to understand both types of bonds one by one.

1- Sigma (σ) bond-

When the axis of orbitals and their axis of joining are the same, the covalent bond formed by their overlapping is called a sigma bond.

The axial or head on the overlapping of two half-filled atomic orbitals forms a sigma bond. The molecular bond thus formed is called a sigma molecular orbital and the electrons constituting it are called sigma electrons.

Following are the ways in which the sigma bond is formed. Types of covalent bonds(sigma and pi)

i- s-s overlapping (sigma bond formation)-

In the s-s overlapping, the axis passing through the nucleus and the axes passing through the overlapping area of s-orbitals is the same as shown in the picture below. s-orbital always forms a sigma bond.

ii- s-p overlapping (sigma bond formation)-

In the s-p overlapping, when the axis passing through the nucleus and the axes passing through the overlapping area of s-orbitals and p-orbitals is the same, a sigma bond is formed, as shown in the picture below.

Overlapping of s-orbitals and p-orbitals always form a sigma bond. The orbital forming a sigma bond can be rotated along the bond axis.

Types of covalent bonds(sigma and pi)

iii- p-p overlapping (sigma bond formation)-

When the axis passing through the nucleus of the orbitals and the axes passing through the overlapping area of p-orbitals and p-orbitals is the same, only a sigma bond is formed, as shown in the picture below. The orbital forming a sigma bond can be rotated along the bond axis.

Types of covalent bonds(sigma and pi)

iv- pz -dz overlapping (sigma bonding)-

When overlapping takes place between pz and dz orbital and axis passing through the nucleus and overlapping area is same, in that case, the sigma bond is formed.

Types of covalent bonds(sigma and pi)

 

2- Pi ( π) bond-

When the line, passing through the nucleus of both the orbitals and the line of joining the orbitals, is not the same (perpendicular to each other), the bond is formed is known as a pi bond.

In another word, the sidewise or lateral overlapping of two half-filled atomic orbitals forms a pi bond.

The molecular orbital thus formed is called a pi molecular orbital and the electrons constituting it, are known as pi-electrons.

The pi-molecular orbital consists of two charge clouds one above and the other below the plane containing the atoms. Pi bond forms by-

i- p-p overlapping (pi bond formation)–

When the lateral overlapping takes place between the p orbitals and the line of the axis and line passing through the overlapping area are different, pi bond is formed shown in the picture below.

The orbital forming a pi bond can not be rotated along the bond axis.

Types of covalent bonds(sigma and pi)

 

ii- d – d overlapping (pi bond formation)-

In the overlapping of d-d orbitals, px and py are perpendicular to the axis. There will be lateral overlapping between px-px and py-py orbitals.

So in between the px and px pi bond is present. Between py and py pi bond is present, whereas between dz and dz sigma bonding is present.

Types of covalent bonds(sigma and pi)

 Example-(Types of covalent bonds(sigma and pi)

In CH₄ (methane) four sigma bonds are present. There is no pi bond in methane.

 

 

In the ethylene molecule (H₂C=CH₂) five sigma and one pi bonds are present.

 

Types of covalent bonds(sigma and pi)

 

Main characteristics of sigma and pi bond-(Types of covalent bonds(sigma and pi)

 

  S.N. Sigma (σ) Bond Pi ( π ) Bond
1 This bond is formed by the axial overlapping of half-filled atomic orbitals.This is formed by the sidewise or lateral overlapping of half-filled atomic orbitals.
2The sigma molecular orbital is symmetric about the internuclear axis.The pi molecular orbital consists of the two charge clouds one above and the other below the plane of the atom.
3The sigma molecular orbital does not contain a nodal plane which contains the internuclear axis.The pi molecular orbital contains a nodal plane which contains the internuclear axis and divides the orbital into two halves.
4This bond is stronger due to a large overlapping of atomic orbitals.This bond is weaker due to relatively lesser overlapping of atomic orbitals.
5The atoms forming a sigma bond can be rotated along the bond axis. The atoms forming a pi bond cannot be  rotated relative to one another

 

Thanks for reading this topic Types of covalent bonds(sigma and pi)

You may also read

Covalent character in ionic bonds

THE HYDROGEN BOND (hydrogen bonding)

Hybridisation in carbon (types and examples)

polarity in covalent bond(dipole moment)

5 thoughts on “Types of covalent bonds(sigma and pi)

Leave a Reply

Your email address will not be published. Required fields are marked *