11th Chemistry Volume · Part

sp ↿⇂ ↿⇂ ↿⇂ ↿⇂ Fig . sp Hybridisation : CH sp d Hybridisation: In the molecules such as PCl , the central atom phosphorus is covalently bound to five chlorine atoms. Here the atomic orbitals of phosphorous undergoes sp d hybridisation which involves its one 3s orbital, three 3p orbitals and one vacant 3d orbital (d z2 ). The ground state electronic configuration of phosphorous is [Ne]3s 3p x 3p y 3p z as shown below. Ground State E 3p x 3p y 3s ↿⇂ ↿ ↿ ↿ 3p z One of the paired electrons in the 3s orbital of phosphorous is promoted to one of its vacant 3d orbital (d z2 ) in the excite state. One 3s orbital, three 3p orbitals and one 3d z2 orbital of phosphorus atom mixes to give five equivalent sp d hybridised orbitals. The orbital geometry of sp d hybridised orbitals is trigonal bi-pyramidal as shown in the figure . . Overlap with 3p z orbitals of chlorine: The 3p z orbitals of the five chlorine atoms linearly overlap along the axis with the five sp d hybridised orbitals of phosphorous to form the five P-Cl σ-bonds, as shown below. Excited state 3d Z 3p 3p y 3p z 3s ↿ E ↿ ↿ ↿ ↿ Hybridised State sp d sp d sp d sp d sp d ↿ ↿ ↿ ↿ ↿ sp d Hybridisation sp d 3p z 3p z 3p z 3p z 3p z sp d sp d sp d sp d ↿⇂ ↿⇂ ↿⇂ ↿⇂ ↿⇂ Fig . sp d Hybridisation : PCl sp d Hybridisation: In sulphur hexafluoride (SF ) the central atom sulphur extend its octet to undergo sp d hybridisation to generate six sp d hybridised orbitals which accounts for six equivalent S-F bonds. The ground state electronic configuration of sulphur is [Ne]3s 3p x 3p y 3p z . Ground State E 3p x 3p y 3s ↿⇂ ↿⇂ 3p z ↿ ↿ One electron each from 3s orbital and 3p orbital of sulphur is promoted to its two vacant 3d orbitals (d z2 and d x2-y2 ) in the excite state. A total of six valence orbitals from sulphur (one 3s orbital, three 3p orbitals and two 3d orbitals) mixes to give six equivalent sp d hybridised orbitals. The orbital geometry is octahedral as shown in the figure. Overlap with 2pz orbitals of fluorine: The six sp d hybridised orbitals of sulphur overlaps linearly with 2p z orbitals of six fluorine atoms to form the six S-F bonds in the sulphur hexafluoride molecule. Excited state 3d Z 3d x –y 3p 3p y 3p z 3s ↿ E ↿ ↿ ↿ ↿ ↿ Hybridised State sp d sp d sp d sp d sp d sp d ↿ ↿ ↿ ↿ ↿ ↿ sp d Hybridisation Fig . sp d Hybridisation : SF sp d 2p z 2p z 2p z 2p z 2p z 2p z sp d sp d sp d sp d sp d F F S F F F F ↿⇂ ↿⇂ ↿⇂ ↿⇂ ↿⇂ ↿⇂ Bonding in Ethylene: The bonding in ethylene can be explained using hybridisation concept. The molecular formula of ethylene is C H . The valency of carbon is . The electronic configuration of valence shell of carbon in ground state is [He]2s 2p x 2p y 2p z . To satisfy the valency of carbon promote an electron from 2s orbital to 2p z orbital in the excited state. Ground State E 2p x 2p y 2s ↿⇂ ↿ 2p z ↿ In ethylene both the carbon atoms undergoes sp hybridisation involving 2s, 2p x and 2p y orbitals, resulting in three equivalent sp hybridised orbitals lying in the xy plane at an angle of 120⁰ to each other. The unhybridised 2p z orbital lies perpendicular to the xy plane. Formation of sigma bond: One of the sp hybridised orbitals of each carbon lying on the molecular axis (x-axis) linearly overlaps with each other resulting in the formation a C-C sigma bond. Other two sp hybridised orbitals of both carbons linearly overlap with the four 1s orbitals of four hydrogen atoms leading to the formation of two C-H sigma bonds on each carbon. Excited state 2p x 2p y 2s ↿ 2p z E ↿ ↿ ↿ Hybridised State sp sp sp 2p z ↿ ↿ ↿ ↿ sp Hybridisation Formation of Pi (π ) bond: The unhybridised 2p z orbital of both carbon atoms can overlap only sideways as they are not in the molecular axis. This lateral overlap results in the formation a pi( π) bond between the two carbon atoms as shown in the figure. 1s sp sp sp sp sp sp 1s 1s 1s ↿⇂ ↿⇂ ↿⇂ ↿⇂ ↿⇂ Fig . sp Hybridisation : C H π π Bonding in acetylene: Similar to ethylene, the bonding in acetylene can also be explained using hybridisation concept. The molecular formula of acetylene is C H . The electronic configuration of valence shell of carbon in ground state is [He]2s 2p x 2p y 2p z . To satisfy the valency of carbon promote an electron from 2s orbital to 2p z orbital in the excited state. In acetylene molecule, both the carbon atoms are in sp hybridised state. The 2s and 2p x orbitals, resulting in two equivalent sp hybridised orbitals lying in a straight line along the molecular axis (x-axis). The unhybridised 2p y and 2p z orbitals lie perpendicular to the molecular axis. Formation of sigma bond: One of the two sp hybridised orbitals of each carbon linearly overlaps with each other resulting in the formation a C-C sigma bond. The other sp hybridised orbital of both carbons linearly overlap with the two 1s orbitals of two hydrogen atoms leading to the formation of one C-H sigma bonds on each carbon. Formation of pi bond: The unhybridised 2p y and 2p z orbitals of each carbon overlap sideways. This lateral overlap results in the formation of two pi bonds ( p y -p y and p z -p z ) between the two carbon atoms as shown in the figure. Excited state 2p x 2p y 2s ↿ 2p z E ↿ ↿ ↿ Hybridised State sp sp 2p y 2p z ↿ ↿ ↿ ↿ sp Hybridisation 1s 1s sp sp sp sp ↿⇂ ↿⇂ ↿⇂