Molecular orbital are of 2 types that is sigma and pi. Here we will discuss how the different types of MO’s formed.
What are the types of Molecular orbital
- s orbital is spherical in shape. Their wave function is same in all the direction.
- p orbital has 2 lobes having + and – sign.
- Overlapping of + sign with + sign results in the formation of bonding MO.
- Overlapping of + sign with – sign results in the formation of antibonding MO.
- The combining atomic orbitals should have comparable energies. For example: 1s combines with 1s. And 2s can combine with 2s but not with 2p orbital.
- They should have proper orientation for the efficient overlapping. For example 2pz can combine with 2pz orbital but not with 2px or 2py orbitals.
- The extent of overlapping should be large.
1. Overlapping of 1s with 1s MO
The overlapping of 1s with 1s results in the formation of sigma 1s and sigma* 1s MOs
2. Overlapping of 2s with 2s MO
The overlapping of 2s with 2s results in the formation of sigma 2s and sigma* 2s MOs
3. Overlapping of 2pz with 2pz MO
The overlapping of 2pz with 2pz occurs along the internuclear axis. This results in the formation of sigma bonds. They are of two types: sigma 2pz and sigma* 2pz MOs
4. Overlapping of 2px with 2px or 2py with 2py MO
The overlapping of 2px with 2px or 2py with 2py occurs sidewise. This results in the formation of Pi bonds. They are of two types: Pi2px and Pi* 2px MOs and Pi2py and Pi* 2py MOs
Difference between Sigma and Pi MOs
- Sigma MO forms when head on overlapping of atomic orbitals occurs along the internuclear axis. While Pi MO forms when lateral overlapping occurs.
- Sigma MO consists of one electron cloud and pi bond consists of two electron clouds lying above and below the plane.
- The sigma MO is symmetrical about the internuclear axis. Pi electron cloud is not symmetrical about the internuclear axis.
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