Types of Hybridization
Types of Hybridization
There are
various types of hybridization involving s, p, and d orbitals. The different
types of hybridization are as under.
sp hybridization:
This type of hybridization involves
the mixing of one s and one p orbital resulting in the formation of two equivalent sp hybrid
orbitals. The suitable orbitals for sp hybridization are s and pz,
if the hybrid orbitals are to lie along the z-axis. Each sp
hybrid orbitals has 50% s-character and 50% p-character. Such a
molecule in which the central atom is sp-hybridized and linked directly
to two other central atoms possesses liner geometry. This type of hybridization
is also known as diagonal hybridization.
The tow sp
hybrids point in the opposite direction along the z-axis with projecting
positive lobes and very small negative lobes, which provides more effective
overlapping resulting in the formation of stronger bonds.
Example of
molecule having sp hybridization
BeCl2:
The ground state electronic configuration of Be is 1s22s2.
In the exited state one of the 2s-electrons is promoted to vacant 2p
orbital to account for its divalency. One 2s and one 2p-orbitals
get hybridized to form two sp hybridized orbitals. These two sp
hybrid orbitals are oriented in opposite direction forming an angle of 180.
Each of the sp hybridized orbital overlaps with the 2p-orbital of
chlorine axially and form two Be-Cl sigma bonds. This is shown below figure.
Sp2 hybridization :
In this hybridization there is
involvement of one s and two p-orbitals in order to form three equivalent sp2
hybridized orbitals. For example, in BCl3 molecule, the ground state
electronic configuration of central boron atom is 1s22s22p1.
In the excited state, one of the 2s electrons is promoted to vacant 2p
orbitals as a result boron has three unpaired electrons. These three orbitals
(one 2s and two 2p) hybridise to form three sp2 hybrid
orbitals. The three hybrid orbitals so formed are oriented in a trigonal planar
arrangement and overlap with 2p orbitals of chlorine to form three B-Cl
bonds. Therefore, in BCl3 the geometry is trigonal planar with CIBCl
bond of 120.
Sp3 hybridization:
This type of
hybridization can be explained by taking the example of CH4 molecule
in which three is mixing of one s-orbital and three p-orbitals of the
valence shell to form four sp3 hybrid orbital of equivalent
energies and shape. There is 25% s-character and 75% p-character in each sp3
hybrid orbital. The four sp3 hybrid orbitals so formed are
directed towards the four corners of the tetrahedron. The angle between sp3
hybrid orbital is 109.5 as shown below.
The structure
of NH3 and H2O molecules can also be explained with the
help of sp3 hybridization.
In NH3, the valence shell (outer) electronic configuration of
nitrogen in the grounds state is 2s2 2p1x 2p1y 2p1z having
three unpaired electrons in the sp3 hybrid orbitals and a lone
pair of electrons is present in the fourth one. These three hybrid orbitals
overlap with 1s orbitals of hydrogen atoms to form three N-H sigma
bonds. As we know that the force of
repulsion between a lone pair and a bond pair is more than the force of
repulsion between two bond pairs of electrons. The molecule thus gets distorted
and the bond angle is reduced to 107 from 109.5. The geometry of such a
molecule will be pyramidal as shown below.
In the case
of H2O molecule, the four oxygen orbitals (one 2s and
three 2p) undergo sp3 hybridization forming four sp3
hybrid orbitals out of which two contain one electron each and the other two
contain a pair of electrons. These four sp3 hybrid orbitals
acquire a tetrahedral geometry, with two corners occupied by hydrogen atoms
while the other two by the lone pairs. The bond angle in this case is reduced
to 104.5 from 109.5 and the molecule thus acquires a V-shape or angular
geometry.
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