63.CHEMICAL BONDING (10)- Covalent Bonding(9)- sp2 Hybridization(4).

sp² hybridization .

The process of mixing of one s- orbital with two p- orbitals in an atom to form three sp² hybrid orbitals of equivalent energy is called sp² hybridization.

 

EXAMPLE  – ETHYⅬENE / ETHENE 

In ethene molecule, the central carbon atom is sp² hybridized.
Carbon (6)  in ground state 1s² 2s² 2p²
One 2s electron is promoted to 2p orbital→ C(6)  1s² 2s¹ 2p³ 
Then, 2s and two 2p hybridize to form three sp² hybrid orbitals.

 

 

Two sp² hybrid orbitals of each carbon atom overlap to form  sp² – sp² bond.This is the sigma bond between two carbon atoms.
However, in this case , a π bond is formed too.The unhybridized p_z orbitals (the p-orbitals which DO NOT take part in hybridization) of both the carbon atoms lie perpendicular to the hybridized orbitals. They overlap laterally/sideways to form a π bond.

The unhybridized p orbital lobes, which overlap laterally to form one π bond , are shown in pink  color in the following figure –

 

NOTE – i)Diagrammatically, the π bond is always shown above and below the sigma bond.Though its shown in two places(these are two regions where p orbital lobes overalp) it symbolizes one π bond only. The two regions show that the electron cloud is above and below the bond axis.

 

The ethene molecule is formed with 4 hydrogen atoms. As we already know that the electron in hydrogen atom is in 1s orbital.Thus, this is a    sp²– s overlap.

 

 

Pictorially the above bonds can be shown as follows –

 

NOTE – The three hybrid orbitals point towards the corners of a triangle at 120^o to each other.They all are in the same plane – in the plane of the bond axis.The p_z orbitals are perpendicular to the bond axis.

sp² hybridization occurs when a carbon atom is attached to 3 groups.In the above example each carbon atom is attached to two hydrogen atoms and another carbon atom.

A sp²  hybrid orbital has 33% s character and 67% p character.

In our next post we shall discuss sp hybridization. Till then,

Be a perpetual student of life and keep learning..

Good day.

References and further reading –

1. http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch02/ch2-3-2.html
2. https://courses.lumenlearning.com/introchem/chapter/sp2-hybridization