If one p orbital of any atom is already involved in sigma bond with another p – orbital of any other atom then the 2” p ~ orbital of that atom overlaps side ways or parallel. This molecular orbital is called Pi orbital, electrons shared are called Pi(n) electron while bond formed is called Pi bond. Two Pi orbitals are formed after overlap. One with lower energy level is called n – bonding orbital while the other one with greater energy is called π – anti-bonding orbital.
Characteristics of Pi Orbitals
i. Pi orbital is formed only when two p – orbitals of two atoms already p – p sigma bond.
ii. Probability of maximum density of electrons is above and below the line joining two nuclei (nodal plane)
iii. Pi orbital is not symmetrical with respect to axis.
iv. Pi orbitals are formed when axis of two Pi orbital are parallel, therefore, two orbitals must be the same.
v. Single bond between two atoms is always a sigma bond but in double or triple bond, first bond is sigma but other one Pi – orbitals bonds.
vi. Sideway overlapping of orbitals is less stable than head to head overlap, therefore π – orbitals are more reactive as compared to sigma orbital. eg. C2H2 (ethane)
An orbital which is under the influence of only one atom nuclei is called “Atomic Orbital”. It is also called “Mono Centric Orbital”.
An orbital which is under the influence of more than one atom’s nuclei is called “Molecular Orbital”. It is also called “Poly Centric Orbital”.