The process of mixing of atomic orbitals of nearly same energy to produce a set of entirely new orbitals of equivalent energy (hybrid orbitals) is known as hybridization. Atomic orbitals of almost the same energy belonging to the same atom or ion can take part in hybridization.. The number of hybrid orbitals formed is always equal to the number of atomic orbitals taking part in hybridization. The hybrid orbitals repel each other and tend to be farthest apart. Hybrid orbitals forms only sigma(σbonds) σ and pi bonds( π bonds )are formed by unhybridised orbitals.
 
 
Sigma bond (σ bonds)
1. The covalent bond formed by the overlap of atomic orbitals along the internuclear axis is called sigma bond.
 
2. The overlapping orbitals are oriented along the internuclear axis.
 
3. The bond is rotationally symmetrical around the internuclear axis
 
4. A as well as p orbitals can form this type of bonds.
 
5. it decide the shape of molecule

6. A single bond contains only one sigma bond while multiple bonds like double bond contain only one sigma bond.

7. sigma bonds have independent existence in molecule

8. It is stronger than a pi bond.
 
Pi  bond (π bonds)
1. The covalent bond formed by the lateral overlap of two p orbitals which are mutually parallel but oriented perpendicular to the internuclear axis is called a pi bond.
 
2. The overlapping orbitals are oriented perpendicular to the inter nuclear axis.
 
3. The bond is not rotationally symmetrical around the internuclear axis.
 
4. Only p orbitals can form this bond.
 

5. It decide the length of the molecule.

6. In the case of the pi bond a single bond contains only one pi bond, whereas multiple  bonds like double bond have two pi bonds and triple bond has three pi bonds.

7. pi bonds are formed additional to sigma bond and not having independent existence.

8. It is weaker than a sigma bond.
						

							
HELLO THERE!
 
To understand easily,
 
If two orbitals suffer head on collision (overlap by head on collision), the resulting bond formed is sigma bond.
 
If two orbitals suffer sidewise overlap, the resulting bond formed is pi-bond.
 
 
=> Pi bond is weaker than Sigma bond, so during Resonance, Pi-bonds are delocalized (not sigma bonds).
 
=> One Sigma bond is present in a single bond (e.g, C-C)
 
=> One Sigma bond and one Pi bond is present in a double bond (e.g, C=C)
 
=> One Sigma bond and two Pi bonds are present in a triple bond.