Hybridisation :
VBT fails to explain the shape &geometryofthe molecules.
Hence, to explain this, Pauling &Slater suplemented VBT withthe concept ofhybridisation. This is a
complete hypotheticalconcept, hybrid orbitals do not exist actually.
According to thisconcept anynumber ofatomic orbitals ofanatomwhichdiffer inenergyveryslightly
mayintermixwith eachother to formnew orbitals called hybrid orbitals. The process ofintermixing of
atomic orbitals ofnearly same energyto produce a set ofentirely new orbitals ofequivalent energyis
known as hybridisation.
Rules of hybridization:
(1) Onlyatomic orbitalsofnearlysame energybelonging to same atomor ioncantakepart is hybridization.
(2) Number ofhybrid orbitals formed is always equalto numbers ofatomic orbitals whichhave taken part
intheprocess ofhybridization.
Characteristics ofhybridization:
(1) Onlyorbitalsofalmost similar energiesand belonging to the same atomor ionundergo hybridization.
(2) Hybridization belongs to orbitals only, not ofelectrons that is vacant orbitals, halffilled orbitals or fully
filled orbitals also canbe participated.
(3) Thenumberofhybridorbitalsproducedisequalto thenumberofpureorbitalsmixedduringhybridization,
e.g. four hybrid orbitals are produced by mixing one s and three p (px
, py
, and pz
) pure orbitals.
(4) In the excited state, the number of unpaired electrons must correspond to the oxidation state of the
centralatomis the molecule.
(5) Bothhalffilledorbitals or fullyfilledorbitals ofequivalent energycaninvolve inhybridization.
(6) Most ofthe hybrid orbitals are similar in shape, size and energy.
(7) Hybrid orbitals form sigma bond only. They do not form π  bonds. Orbitals involved in π bond
formationdo not participate inhybridization.
(8) Hybridizationnever takesplace inanisolated atombut it occurs onlyat the time ofbond formation.
(9) The hybrid orbitals are distributed in space as a part as possible resulting in a definite geometry of
molecule.
(10) Hybridized orbitalsprovide efficient overlapping thanoverlapping bypure s, p ane dorbitals dueto the
same energy.
(11) Hybridised orbitals possess lower energy.
(12) Depending upon the no. & nature of orbitals under going hybridisation, the molecule has a regular
geometryifallthe hybrid orbitals after overlapping containshared pair ofe
s i.e. There areno orbitals
containing . Some pairs is thevalence shell.
CHEMISTRY Theory Notes on Chemical Bonding-V