# Hybridization of oxygen in Nitrate ion and the location/bond of nitrogen's lone pair

I have tried to apply the rules and basics that I learnt so far. But I am confused about the hybridization of oxygen atoms which are making the single bond in nitrate ion.

Following are the steps I used. The average bond order of 4/3 makes the molecule unstable.

Based on the steps, the single bonds are made of $\ce{sp^3}$ of oxygen and $\ce{sp^2}$ of nitrogen, the bonds are sigma bonds. However that doesn't seem like the case. If I look at $\ce{HNO3}$ dissociation equation in the water, lone electron pair of nitrogen is entirely shared with (co-ordinative covalent bond) one of the oxygens making a single bond.

$\ce{ HNO3(aq) -> H+(aq) + NO3^{-}(aq) }$

But considering $\ce{NO3}$ ion individually, without thinking about nitric acid, I can't find the long pair to be in the same type of co-ordinative bond. Isn't there an unbonding sp2 electron with nitrogen (probably one from the lone pair)?

The other issue, why isn't oxygen hybridizing to be $\ce{sp^3}$ here? What am I doing wrong here?

• You indeed can think that these two $\ce{O-}$ are sp3-hybdiridzed. But I would rather explicitly call them $\ce{O-}$ rather then just $\ce{O}$. – Wildcat Jul 26 '15 at 13:09
• nintrate-ion is isoelectronic to carbonate ion. The bonding is very similar except that in nitrate due to positive charge on nitrogen, the bonds are stronger. – permeakra Jul 16 '16 at 10:58