Sigma and Pi Bond
Hybridization
sp3
sp2
sp
IIT Questions
Sigma and Pi Bond Types of covalent bond Lets see how molecular orbital can form bonding. What you need to know is s subshell is spherical in shape and p is dumble in shape. p has three orientations p
x
,p
y
and p
z
. There are two main types of covelent bonds.
1. Sigma bond
2. Pi bond
1.Sigma Bond : A sigma bond is formed by the linear or end-to-end overlap of orbitals.
(2) Pi- Bond : A pi bond is formed by parallel or side-by-side overlap of p orbitals.
Difference between Sigma Bond and Pi Bond :
(1) Sigma bond being direct overlap , electrons are strongly held than side wise overlap of Pi-electrons. Hence Pi electrons are more easily broken and reactive than sigma electrons. Sigma bond is stronger than Pi bond.
(2) Rotation of atoms is not possible around a Pi bond. If any attempt is made to rotate, the lobes of p orbitals will no longer be co-planer and will not overlap to form pi bond. This restriction in rotation around a pi bond is responsible for Cis and Trans isomerism in alkanes.
Hybridization: Carbon has Six Electrons. Its electronic configuration is 1S
2
2S
2
2P
2
. In more detail we can write 1S
2
2S
2
2px
1
2py
1
2pz
0
. When energy supplied to carbon atom in the form of heat or light the 2S orbital electron gains energy and jumps to higher energy shell that is occupies vacant 2pz
0
. This is called Excited state of Carbon atom. So we can write 1S
2
2S
1
2px
1
2py
1
2pz
1
. Now we have singly occupied 4 subshell 2s and 3p (px,py,pz).
The excited state orbitals mixed (hybridized) to give four new equivalent orbitals. These new orbitals are known as sp
3
orbitals as they are formed by mixing one pure s orbital and three p orbitals.
This process of mixing of pure orbitals to give a set of new equivalent orbitals is termed as Hybridization.
C(Hybridized State) = 1s
2
2(sp
3
)
1
2(sp
3
)
1
2(sp
3
)
1
2(sp
3
)
1
Depending upon the number of hydrogen atoms available for bonding either 2s electron mixes with 2p electron to form 4 equivalent energy orbital,3 equivalent energy orbital or 2 equivalent energy orbital. we call them sp
3
,sp
2
and sp hybridization respectively.
Whenever carbon is bonded to four other atoms or groups ( as in methane ) , it uses sp
3
hybride orbitals.
Whenever carbon is bonded to three other atoms or groups ( as in ethylene ) , it uses sp
2
hybride orbitals.
Whenever carbon is bonded to two other atoms or groups ( as in acetylene ) , it uses sp hybride orbitals.
Please Ref. IIT Question Set , we will soon publish how to attempt IIT Question related to hybridization.
