Question

What is the formal charge on atom in carbonate and nitric acid?

Answer 1

The charge assigned to an atom in a molecule is a formal charge.

Formal charge $\left(FC\right)$ is given by the formula,

$FC=V-N-B/2$

Where,

$V=$ Number of valence electrons

$N=$ Number of non-bonding electrons

$B=$ Total number of electrons shared in covalent bonds.

The formal charge of $N$ in $NO{2}^{-}$ is

$FC=5-2-6/2=0$

For the LHS oxygen the $FC$ is-

$FC=6-6-2/2=-1$

For the RHS oxygen the FC is-

$FC=6-4-4/2=0$

The carbonate ion $\left[C{O}_3{}^{2-}\right]$ has an overall charge of -2. In the carbonate ion, the carbon atom is bonded with a double bond to an oxygen atom, and with single bonds to two oxygen atoms.

Formal charge on oxygen bonded with the double bond = $6-4-1/2\left(4\right)=0$

Formal charge on oxygen atoms bonded with single bond = $6-6-1/2\left(2\right)=-1$

In $HN{O}_3$

The nitrogen atom carries a charge of $+1$, and one oxygen atom carries a charge of $-1.$