Why don't PH3, AsH3, SbH3 & BiH3 participate in hybridization like NH3? Please explain how does increase in size of central atom affect hybridization.
Is the same trend followed for group 13,14,16,17?
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Unlike NH3, for hybridisation you need to have bonding orbitals having similar energy (not having very large difference) and also the bonding atom should have a higher electronegativity. Due to high electronegativity , the central atom has greater tendency to attract the electrons. In the case such as PH3 , AsH3 etc. the central atom being a non-metal also they have similar electronegativity as that of Hydrogen. The central atom in each case have vacant d-orbital due to which if small amount of energy is given out the electrons excite to d-orbitals and can participate in d pi -p pi bonding.
Here the size of central atom is huge compared to that of Hydrogen, so the hydrogen atoms approach from the axial side hence have a bond angle close to 90 degrees (p-orbitals are axial and the orbitals are mutually perpendicular to each other).
When size increases, the efficiency of p pi-p pi overlap decreases and the the lone pair(if any) on atoms are unable to take part in hybridization.