Question

why PCl5 is trigonal bipyramidal where as IF5 is square pyramidal?....plz reply..thankyou!

Answer 1

sanya
PCl5 is a compound which has P as a central atom
however in IF5 I is a central atom which has a extra lone pair which adjusts itself as square pyramidal and PCl5 as Trigonal bipyramidal

Answer 2

In case of $\mathrm{PCl}_{5}$, P has 5 valence electrons in $3 s^{2}, 3 p^{3}$ orbitals. To make 5 bonds with 5 Cl atoms, it will excited one of its electron from 3s to 3d therefore the hybridization will be $\mathrm{sp}^{3} \mathrm{d}$.

And with $\mathrm{sp}^{3} \mathrm{d}$ hybridization the geometry will be trigonal bipyramidal whereas in case of $\mathrm {IF_{5}}$, the Iodine atom has 7 valence electrons in $5 s^{2}, 5 p^{5}$.

Hence to make 5 bonds with 5 Cl, two electrons from 5p will excited to 5d and the hybridization will be $\mathrm{sp}^{3} \mathrm{d}^{2}$ with one lone pair on I atom that gives the square pyramidal geometry to molecule.