[coolviks]

During the hybridization(excitation) of pcl5 one electron from 3s orbital jumps to 3d orbital providing 5 vacant space for 5 chlorine atoms. My question is that why the electron does not jump to 4s orbital because according to aufbau's principle 4s orbital comes before 3d orbital. plzz help..

[magician4]

mixing orbitals to result in hybrids not only offers new opportunities for electrons to store, but also determines what shape this hybrid has to have: the rule of "conservation of symmetry" requires that the sum total of symmetries of parent orbitals equals the sum total of symmetries of resulting orbitals .

now, if you wish to construct the 5 hybrid orbitals of a trigonal-bipyramidal structure by using 1 * s , 3 * p and 1 * "?" , using another s ( i.e. another spherical symmetry) for "?" would lead you exactly nowhere: you need someting "with a direction" ( like, for example, a d-orbital) instead

that's why s is of no use , and hence isn't used for PCl₅ , even though 4s in the pure atom of phosphorus, in the oxidation state of zero , in vacuum,  might look more inviting at a first glance.

regards

Ingo

[Vidya]

During hybridization ,orbitals of nearly same energy are mixed together to give hybridized orbitals.4s orbitals are higher in energy than n=3 orbitals (3s,3p and 3d).

Only when we start filling electrons and have more nuclear charge which is poorly shielded for 4s electrons then the electron goes in 4s first because it comes closer to nucleus.

[coolviks]

Thank you so much vidya and magician4.. This really clears my concept of hybridization.