Question

Which of the following has trigonal pyramidal ?
(A) $PC{l_5}(s)$
(B) $PC{l_5}(g)$
(C) $PB{r_5}(s)$
(D) ${\left( {S{F_5}} \right)^ + }$

Answer 1

Atoms bond together to form molecules that have different sizes and shapes. Molecular shape determines several properties of substances like polarity, reactivity. Physical and chemical properties depend on the geometry of a molecule.

Complete step by step answer:
Atoms are usually not capable of free existence except noble gases. However, a group of atoms is found to exist together as one species with characteristic properties. Such a group is called a molecule. The attractive force which holds various constituents (atoms, ions) together in a molecule is called a chemical bond.
The shape of a molecule depends upon the number of valence shell electron pairs (bonded and non-bonding electron pairs) is referred to as a bond pair while the unshared/nonbonding pair of electrons on an atom is referred to as a lone pair.
Electron pair around the central atom exert repulsive force on one another as possible so that the forces of repulsion are minimised the shape of the molecules are different
$PC{l_5}(s)$ decompose and forms $2PCl \to {\left[ {PC{l_4}} \right]^ + } + {\left[ {PC{l_6}} \right]^ - }$ in which ${\left[ {PC{l_4}} \right]^ + }$ having tetrahedral shape and${\left[ {PC{l_6}} \right]^ - }$ have octahedral shape so $PC{l_5}(s)$ not an trigonal pyramidal shape.
$PC{l_5}$behaves as a nucleophile in which phosphorus has more than eight electrons in the outermost shell after sharing electrons with chlorine atoms. And the shape of the $PC{l_5}$molecule is trigonal pyramidal in which $s{p^3}d$ hybridization occurs. One$s$, two $p$and $d$orbital forms hybrid orbitals having equal energy form trigonal pyramidal shape.
So option B is the correct answer.

Note:
Bond angle- the angle between the lines representing the directions of the bond is called the bond angle. It can be measured by X-ray analysis or by some other spectroscopic methods such as infra-red spectroscopy.
Number of domains around the central atom determines the geometrical arrangement.