Question

The shape of $Xe{{O}_{2}}{{F}_{2}}$ molecule is

A) Trigonal bipyramidal

B) Square planar

C) Tetrahedral

D) See-Saw

Answer 1

The shape of $Xe{{O}_{2}}{{F}_{2}}$ is based on the number of atoms joined to the central atom. Not only atoms, but lone pairs are also considered for the shape. For finding the shape of the compound, the total number of electron pairs and the number of lone pairs should be calculated with the help of valence electrons, the number of bonds, etc.

Complete answer:

Both the VSEPR theory and the concept of hybridization are applied to predict the molecular geometries of xenon compounds.

According to the VSEPR theory, the shape of the molecule is predicted by the total number of electron pairs (lone pairs + bond pairs) in the valence shell of the central Xe atom.

To calculate the total number of electron pairs:

$\dfrac{\text{valence electrons of central atom + number of bonded atoms}}{\text{2}}$

Since 2 fluorine atoms form a single bond and 2 oxygen atoms which form the double bond.

With the above formula: $\dfrac{8+(2+4)}{2}=\dfrac{8+6}{2}=7$

Hence, there are 7 electron pairs.

Since there are 2 fluorine atoms and 2 oxygen atoms joined to xenon. So, there will be a 6 bond pair of electrons.

Now for calculating the number of lone pairs in the compound: -

total number of electron pairs –number of bond pairs.

Lone pairs= 8-7=1

Hence, in the compound, there are 1 lone pair.

Depending on the number of $Xe-F$ and $Xe=O$ covalent bonds to be formed, the requisite number of electrons of the $5p-orbital$ valence shell of Xe gets unpaired and promoted to the vacant $5d-orbitals$ followed by hybridization.

Since there are seven electron pairs and one oxygen atom has 2electron pairs. Hence the hybridization will be $s{{p}^{3}}d$ .

So, the hybridization is $s{{p}^{3}}d$ and it has one lone pair, the geometry of $Xe{{O}_{2}}{{F}_{2}}$ will be Trigonal bipyramidal and shape will be See-Saw.

So, the correct answer is Option (D).

Note: Whenever you are drawing the compound structure the number of lone pairs should also be considered. In this example also there are 4 atoms with xenon, so you could get confused between tetrahedral, square planar shape, and Trigonal bipyramidal.