Question

How do you draw the orbital overlap for PH3? How do you know the angle of which to draw the bonds?

Answer 1

Ans:

To draw the orbital overlap for any molecule one needs to find out the hybridization of the molecule first.

A simple way to identify the hybridization for mono centred molecule is

H = ½ [V+M-C+A]

Where, H = Hybridization/ no. of orbitals involved in hybridization

V = total number of valence electrons of the central atom (For P = 5)

M = Number of monovalent atom linked to central atom (for PH₃, here it is 3)

C = Charge on cation (not applicable for PH₃)

A = charge on anion (not applicable for PH₃)

H	4	3	2
Hybridization	sp3	sp2	sp

So, for PH₃, H = ½ [5+3] = 4.

So the hybridization of the central atom (P) is sp3.

So, shape of the molecule is tetrahedral.

The normal bond angle for a regular tetrahedron is 109^o.28'.

But here, there will be deviation because of the presence of lone pair on ‘P’ (Refer to the fact that lone pair-lone pair repulsion > lone-pair-bond pair repulsion > bond pair-bond pair repulsion). So HPH bond angle will be less than 109^o.28'. (for the exact value of bond angle one needs to do the experiment).

So the orbital diagram of PH₃ will be;