Question

Calculate $x + y + z$ for ${H_3}P{O_3}$ where $x$ is the number of lone pair $y$ is the number of σ bonds and $z$is the number of π bonds.
A. $5$
B. $14$
C. $13$
D. $12$

Answer 1

Hint: The shape of the molecules depends upon the number of valence electron shell pairs which can be bonded or non-bonded, around the central carbon atom. The valence shell is taken as a sphere with the electrons localising on the spherical surface at maximum distance from one another.

Complete step by step answer:
According to the VSEPR theory, which stands for Valence shell electron pair repulsion theory by explaining the important differences between lone pairs and bond pairs of electrons. The lone pairs are centralised on the atom and are the electrons which are not being shared with any other species. However, bonding pairs are shared between the species and belong to both of them on the basis of their electronegativities.

According to VSEPR,
We know, Electronic configuration of phosphorus will be
$1{s^2}2{s^2}2{p^6}3{s^2}3{p^3}$
We know, Electronic configuration of Oxygen
$1{s^2}2{s^2}2{p^5}$
We know, Electronic Configuration of Hydrogen
$1{s^1}$
So, The Number of lone pair will be six
Number of σ bonds will be six
Number of π bonds will be one
Hence, $6 + 6 + 1 = 13$

So, the correct answer is Option C.

Note: VSEPR theory has a lot of drawbacks . It does not accurately predict the geometry of the transition metal species and shapes of isoelectronic compounds
Also, the type of theory assumes that the lone pair do not participate in the structure in any way, however, they do contribute to the stereochemistry. VSEPR does not account for this participation. Hence, a revised version and more modern theory was required. Called crystal field theory, it works on the principle of wave function and considers electrons as waves.