Question

What is the formal charge of \[N\] in \[HN{O_3}\]\[?\]

Answer 1

Hint: First we have to know what is the formal charge of an atom (\[FC\]). Then we can calculate an atom's formal charge using the equation \[FC = VE - \left[ {LPE - \dfrac{1}{2}(BE)} \right]\], where, \[VE\]is the number of valence electrons on the free atom, \[LPE\] is the number of lone pair electrons on the atom in the molecule , and \[BE\] is the number of bonding (shared) electrons around the atom in the molecule.

Complete answer:
\[HN{O_3}\] is the chemical formula of Nitric acid which is colourless, fuming, and highly corrosive liquid \[\left( {freezing} \right.\] point \[ - {42^o}C\left[ {{{44}^o}F} \right]\], boiling point is \[\left. {{{83}^o}C\left[ {{{181}^o}F} \right]} \right)\].
The valence electrons of nitrogen in its compounds are all \[s{p^3}\]hybridized orbitals. The formal charge on \[N\] is usually \[ - 1\] for an anion, \[0\] for a neutral compound, and \[ + 1\] in cations.
A formal charge is the charge assigned to an atom in a molecule, assuming that electrons in all chemical bonds are shared equally between atoms, regardless of relative electronegativity.
An example \[C{O_2}\]means carbon dioxide \[(O = C = O)\], each \[O's\] formal charge would be calculated by: \[6(valence)0 - 4(lone\;electrons) - 2(bonds)\].
A reasonable Lewis structure is \[H - O - \mathop N\limits^ + \left( { = O} \right){O^ - }\]. Which is also represent as

 , where each \[ \bullet \]represents an electron.
Since, the oxygen atom has a formal negative charge, and the nitrogen atom is quaternized and bears a formal charge. Of course, the molecule is neutral, and the Lewis structure reflects this. When nitric acid dissociates we get the following reaction
\[HN{O_3}(aq) + {H_2}O(l) \to {H_3}{O^ + } + N{O_3}^ - \]
Here, nitrogen has \[5\] valence electrons and the number of lone pair electrons on nitrogen in the molecule is \[0\] and \[8\]the number of bonding (shared) electrons around the atom in the molecule.
Then the formal charge of \[N\] in \[HN{O_3}\] \[ = 5 - 0 - \dfrac{1}{2} \times 8 = + 1\].

Note:
Note that nitric acid is a common laboratory reagent and an important industrial chemical for the manufacture of fertilizers and explosives. It is toxic and can cause severe burns. The overall charge on the ion is still −1, but there is again formal charge separation in our representation of the anion.