A sigma bond is defined as a covalent bond formed by axial overlapping of axial orbitals.
This strong greater than pi bonds.
As an example, methane molecule contains bonds, covalent bonds by the overlapping of bonding orbitals along internuclear axis end to end orbitals known as head overlapping.
These are the overlapping orbitals: s-s, s-p, and p-p overlapping.
s-s overlapping: Two half-filled s orbital which interact along the internuclear axis.
s-p overlapping: Take between half-filled s orbitals of one atom and half-filled p-orbitals.
p-p Overlapping: Overlapping between half-filled p-orbitals.
These bonds exist independently and free rotation is seen in them.
It is involved in the control of geometry.
One sigma bond is involved in pi bond and triple bonds.
These bonds are reactive and the shape of a molecule is determined by these bonds.
Pi bonds:
A pi bond is defined as an atomic orbital intersecting positive directional to the internuclear axis.
The atomic orbitals converge axis parallel to each other and perpendicular to the central axis.
These are formed through lateral overlap half-filled atomic orbitals.
Two pure or unhybridized orbitals are alternating orbitals.
It also exists along with sigma bonds.
No rotation exists in these bonds.
It is less strong than sigma bonds.
It is not involved in the control of geometry.
One pi bond is observed in double bonds and in a triple bond, there are two pi bonds.