Question

What is the geometry of $XeO{F_2}$?
A.Pyramidal
B.T-Shaped
C.Octahedral
D.Tetrahedral

Answer 1

We have to know that the molecular geometry of a molecule could be predicted using VSEPR theory. With the help of VSEPR theory, we could get the steric number of the molecule. We can define steric number as the sum of the total bond pairs
linked to the central atom and total lone pairs present in the central atom.

Complete answer:
VSEPR theory stands for valence shell electron pair repulsion theory. We saw that the VSEPR theory can be used to predict the geometry of the molecule with the help of the number of electron pairs enclosing the central atom of the molecule. Based on this theory, we have to draw the Lewis structure of the molecule and then we have to calculate the steric number of the molecule.
We can draw the Lewis structure of $XeO{F_2}$ as,
The number of valence electrons in xenon= $1 \times 8 = 8$ electrons
The number of valence electrons in oxygen= $1 \times 6 = 6$ electrons
The number of valence electrons in fluorine= $2 \times 7 = 14$
The total number of valence electrons in $XeO{F_2}$ is twenty eight electrons.
The Lewis structure of $XeO{F_2}$ is,

Let us now predict the steric number. We can write the formula of steric number as,
$\text{Steric Number} = \text{No.of bonded pairs in central atom} +\text{ Number of lone pairs present in central atom}$
From the Lewis structure, let us now calculate the steric number. We can see that two atoms of fluorine and one atom of oxygen are bonded to the central xenon atom, so the number of bonded pairs in the central atom is three. In xenon, two lone pairs are present.
So, the steric number is calculated as,
$\text{Steric Number} = \text{No.of bonded pairs in central atom} +\text{ Number of lone pairs present in central atom}$
Now we can substitute the known values we get,
$Steric number = 3 + 2$
On simplification we get,
$Steric number = 5$
So, the steric number is five. For steric number five with zero lone pairs on the central atom, the molecular geometry is T-Shaped.
The molecular geometry of the $XeO{F_2}$ molecule is T-shaped.

Option (B) is correct.

Note:
We have to know that with the help of steric numbers, we can also predict the bond angle and hybridization on the central atom. For steric number five, the hybridization of the central atom would be $s{p^3}d$ and the electron pair geometry would be trigonal bipyramidal.