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 pz 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 120o to each other.They all are in the same plane – in the plane of the bond axis.The pz 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,
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References and further reading –