Question

In $P{O}_4^{3-}$ ion the formal charge on the oxygen atom of $P-O$ bond is

• A. $+0.75$
• B. $-0.75$
• C. $+1$
• D. $-1$

Answer 1

The correct option is D $-1$

Formal charge

The formal charge of an atom in a polyatomic molecule or ion may be defined as the difference between the number of valence electrons of that atom in an isolated or free state and the number of electrons assigned to that atom in the Lewis structure.

It is expressed as:

Formal charge $=V-U-S/2$

Where,

$V=\left(\text{Total number of valence electrons in the free atom}\right)$

$U=$Total number of non-bonding electrons

$S=$ Total number of bonding or shared electrons

Formal charge on oxygen of $P-O$ bonds in $P{O}_4^{3-}$ ion

Using the above formula on any of the oxygen atoms marked as $2,3$ or $4$ in $P{O}_4^{3–}$ ion:



Total number of valence electrons in $O$ atom,

$V=6$

Total number of non-bonding electrons,

$U=6$

Total No. of bonding electrons, $S=2$

So, formal charge $=6–6-\left(2/2\right)=-1$

The formal charge on the oxygen atom of $P–O$ bond is $-1.$

Hence, the correct choice is $\left(B\right).$