is sp – s sigma with bond length pm. The H–C–H bond angle is . ° while the H–C–C angle is °. The formation of sigma and pi bonds in ethene is shown in Fig.
Formation of sigma and pi bonds in ethene sp Hybridisation in C H : In the formation of ethyne molecule, both the carbon atoms undergo sp -hybridisation having two unhybridised orbital i.e., p y and p x . One sp hybrid orbital of one carbon atom overlaps axially with sp hybrid orbital of the other carbon atom to form C–C sigma bond, while the other hybridised orbital of each carbon atom overlaps axially with the half filled s orbital of hydrogen atoms forming σ bonds. Each of the two unhybridised p orbitals of both the carbon atoms overlaps sidewise to form two π bonds between the carbon atoms. So the triple bond between the two carbon atoms is made up of one sigma and two pi bonds as shown in Fig.
Hybridisation of Elements involving d Orbitals The elements present in the third period contain d orbitals in addition to s and p orbitals. The energy of the d orbitals are comparable to the energy of the s and p orbitals. The energy of d orbitals are also comparable to those of s and p orbitals. As a consequence the hybridisation involving either s , p and d or d , s and p is possible.
However, since the difference in energies of p and s orbitals is significant, no hybridisation involving p , d and s orbitals is possible. The important hybridisation schemes involving s , p and d orbitals are summarised below: Fig. . Formation of sigma and pi bonds in ethyne (i) Formation of PCl (sp d hybridisation): The ground state and the excited state outer electronic configurations of phosphorus (Z= ) are represented below.
sp d hybrid orbitals filled by electron pairs