donated by five Cl atoms. Shape of molecules/ ions Hybridisation type Atomic orbitals Examples Square planar dsp d + s + p ( ) [Ni(CN) ] – , [Pt(Cl) ] – Trigonal bipyramidal sp d s + p ( )+ d PF , PCl Square pyramidal sp d s + p ( )+ d ( ) BrF Octahedral sp d d sp s + p ( )+ d ( ) d ( )+ s + p ( ) SF , [CrF ] – [Co(NH ) ] + Now the five orbitals ( i.e., one s , three p and one d orbitals) are available for hybridisation to yield a set of five sp d hybrid orbitals which are directed towards the five corners of a trigonal bipyramidal as depicted in the Fig. . .
Fig. . Trigonal bipyramidal geometry of PCl molecule It should be noted that all the bond angles in trigonal bipyramidal geometry are not equivalent. In PCl the five sp d orbitals of phosphorus overlap with the singly occupied p orbitals of chlorine atoms to form five P–Cl sigma bonds.
Three P–Cl bond lie in one plane and make an angle of ° with each other; these bonds are termed as equatorial bonds. The remaining two P–Cl bonds–one lying above and the other lying below the equatorial plane, make an angle of ° with the plane. These bonds are called axial bonds. As the axial bond pairs suffer more repulsive interaction from the equatorial bond pairs, therefore axial bonds have been found to be slightly longer and hence slightly weaker than the equatorial bonds; which makes PCl molecule more reactive.
(ii) Formation of SF (sp d hybridisation): In SF the central sulphur atom has the ground state outer electronic configuration s p . In the exited state the available six orbitals i.e., one s , three p and two d are singly occupied by electrons. These orbitals hybridise to form six new sp d