Is the formula given for hybridisation i.e. (total valenceelectrons)/8 always applicable? If not what are its limitations and how dowe solve it then

Dear student: If you can assign the total electron geometry (geometry of all electron domains, not just bonding domains) on the central atom using VSEPR, then you can always automatically assign hybridization. Linear -sp- the hybridization of onesand oneporbital produce two hybrid orbitals oriented180∘apart.

Trigonal planar -sp2- the hybridization of onesand twoporbitals produce three hybrid orbitals oriented120∘from each other all in the same plane.

Tetrahedral -sp3- the hybridization of onesand threeporbitals produce four hybrid orbitals oriented toward the points of a regular tetrahedron,109.5∘apart.

Trigonal bipyramidal -dsp3orsp3d- the hybridization of ones, threep, and onedorbitals produce five hybrid orbitals oriented in this weird shape: three equatorial hybrid orbitals oriented120∘from each other all in the same plane and two axial orbitals oriented180∘apart, orthogonal to the equatorial orbitals.

Octahedral -d2sp3orsp3d2- the hybridization of ones, threep, and twodorbitals produce six hybrid orbitals oriented toward the points of a regular octahedron90∘apart.

You can also find the hybridization of the atom by finding its steric number:

steric number= no of atoms bonded (to the atom you are finding the hyb. of) + lone pairs with that atom.

if Steric no comes to be 4, there is sp3 hybridization in the atom.

if steric no comes to be 3, there is sp2 hybridization in the atom.

if steric no comes to be 2, there is sp hybridization in the atom.

Regards

Sumit