Question

The geometry of the atoms in the species $PCl_4^ + $ is best described as:
A.Tetrahedral
B.See-saw
C.Square
D.Trigonal bipyramidal

Answer 1

Hint: In this question, we have to identify the geometry of the atoms of $PCl_4^ + $.Geometry is the arrangement of atoms and bonds in the molecule. It can be identified based on the hybridization of the molecule. Various theories are involved to determine the shape of the molecules. $PCl_4^ + $ is the cation of $PC{l_5}$ (phosphorus pentachloride). In the solid state, phosphorus pentahalide exists as an ionic solid in the form ${\left[ {PC{l_4}} \right]^ + }\,\,{\left[ {PC{l_6}} \right]^ - }$.

Complete step by step answer:
Now we will discuss the given options in detail.
$PCl_4^ + $ cation is a $A{X_4}$ type ion. It has four bonding pairs with no lone pairs. The phosphorous atom in $PCl_4^ + $ is $s{p^3}$ hybridized and the geometry is tetrahedral. The bond angle is close to ${109.5^0}$.
Second option is see-saw. See-saw is a type of molecular geometry in which there are four bonds attached to a central atom. For a molecule to be in seesaw geometry it should have a lone pair. Since $PCl_4^ + $ has no lone pair and it is $s{p^3}$ hybridized its atom will not be in see-saw geometry.
Third option is square planar. The square planar molecular geometry in chemistry tells us about the stereochemistry which means spatial arrangement of atoms adopted by certain chemical compounds. From the name itself we can say that molecules of this geometry have their atoms positioned at the corners of a square about a central atom on the same plane. Since $PCl_4^ + $ is $s{p^3}$ hybridized, its geometry of atoms cannot be square planar.
Fourth option is trigonal bipyramidal. A trigonal bipyramid formation is a type of molecular geometry in which one atom is present at the center and 5 more atoms are present at the corners of a triangular bipyramid. This is one geometry for which the bond angles surrounding the central atom are not identical because there is no geometrical arrangement with five terminal atoms in equivalent positions. Since, $PCl_4^ + $ has four atoms bonded to the central atom, its geometry of atom cannot be trigonal bipyramidal.
After discussing in detail we can say that the geometry of the atoms in the species $PCl_4^ + $ is described as tetrahedral.
Hence, the correct option is (A).

Note:
The concept of geometry comes from the concept of hybridization. Hybridization is defined in terms of intermixing of the orbitals of an atom having nearly the same energy to give exactly equivalent orbitals with same energy, identical shapes and symmetrical orientations in space.