A hybrid orbital results from the mixing of different atomic orbitals on the same atom. The atom can form stronger covalent bonds using these hybrid orbitals. When atomic orbitals overlap they form two types of covalent bonds: sigma and pi.
Sigma bonds occur when two atomic orbitals overlap along the bond axis and this bond always forms in a single covalent bond. Pi bonds occur when two pi orbitals overlap sideways and they only form within a double or triple bond. A double bond contains one sigma bond and one pi bond, whereas a triple bond contains one sigma bond and two pi bonds.
There are three types of hybridisation: sp3, sp2 and sp.
Sp3 hybridisation forms a tetrahedral structure with 109.5° between the orbitals. Carbon undergoes sp3 hybridisation when it forms four single bonds and produces four equal orbitals. An example of sp3 hybridisation is methane, CH4.
Sp2 hybridisation forms a triangular planar shape with 120° between the orbitals. Carbon undergoes sp2 hybridisation when it forms a double bond, producing three equal orbitals. An example of sp2 hybridisation is ethene, C2H4.
Sp hybridisation forms a linear structure with 180° between the orbitals. Carbon undergoes sp hybridisation when it forms a triple bond, creating two equal orbitals. An example of sp hybridisation is ethyne, C2H2.