Hybridization is the mixing of orbitals as the same atom to form hybrid orbitals.
✠Simple VB theory has the following deficiencies
1. prediction of bond angles is poor. Eg:- H2O, NH3.
2. Number of bonds that may be formed is not predicted accurately. Eg:- Tetravalency of Carbon.
✠ Both deficiencies are over come when hybridization of AO’s (called modified VB theory) is considered.
➲Hybridization is the mixing ( formation of linear combinations ) of orbitals as the same atom to form hybrid orbitals. Eg:- SP, SP²,SP³.
➲ Hybridization involves:
① Promotion of electron in the valance shell to higher orbitals (the energy required for promotions is recovered by subsequent formation of bond).
② Mixing (linear combinations) of orbital to form mixed orbitals (LCAO’s) called hybrid orbitals on the same atom.
ⅰ. Hybridizatiòn phenomenon occurs only in the combined state.
ⅱ. Hybridizatiòn leads to more efficient overlapping
Example of Hybridization :
Hybridiztions in Carbon atom is envisaged as shown below-
Carbon G.S. Valence
Promoted atom (Excited state) E.C
Different types of Hybridization from promoted atom:
SP³- Tetrahedarl hybridizatioņ
SP²- Planner hybridizatioņ
SP- Linear hybridizatioņ
LCAO wave functions of hybrid orbital:
h1 = S+Px+Py+ Pz
h2 = S-Px-Py+ Pz
h3 = S-Px+Py+ Pz
h4 = S+Px-Py+ Pz (Other combination are also possible)
h1 = S+2Px
h2 = S+(3/2)½Px-(1/2)½Py
h3 = S-(3/2)½Px-(1/2)½Py
h1 = S+P3
h2 = S-P3
Note:- Other combinations of orbitals are also possible
* The hybridizatioņ of ‘N’ atomic orbitals (AO’s) always results in the formation of ‘N’ hybrid orbitals.
This is to conserve orbitals electron density as each orbital is a one-electron wave function.
* In the ideal hybrids the orbital contributions are integers. In actual molecules the contribution of AO to hybrides may be of functional values. These may be inferred from observed bond angles.
• Effect of Hybridizatioņ on molecular properties:
Molecular properties that may be affected by the type of Hybridizatioņ include-
1. Bond angles
2. Bond lengths
4. Molecular moments
For explaining the characteristic shapes of polyatomic molecules. Pauling introduced the concept of hybridisation of atomic orbitals. The process of hybridisation involves the mixing of orbitals of almost similar energy belonging to same atom, to form the same number of orbitals of exactly equal energy.
sp,sp2. sp3 hybridisations of atomic orbitals ‘of Be, B, C, N and O are used to explain the formation and geometrical shapes of molecules like BeCl2, BCl3, CH4, NH3 and H20.
In case of 3rd period elements, the energy of 3d orbitals are comparable to the energy of 3s and 3 p orbitals as well as to the energy of 4s and 4p orbitals. As a result of this, hybridisation involving either 35, 3 p and 3d or 3d ,43 and 4p is possible, For example, P in PCl5 is sp3d hydridised.
In PCl5 the two axial bonds are slightly elongated and hence, slightly weaker than equitorial bonds. Due to this PCI 5 is more reactive.