Chemical Bonding: HNO₃ Lewis Structure

Drawing the Lewis Structure for HNO₃

Viewing Notes:

• The HNO₃ Lewis structure is easier to think of if you consider it NO₃ with an H bonded to one of the oxygen atoms.
• In HNO₃ Lewis structure Nitrogen (N) is the least electronegative atom and goes in the center of the Lewis structure.
• Check the formal charges to be sure that each atom has a formal charge of zero. In this case the formal charges will be closer to zero if you place a double bond beteween the Nitrogen atom and the Oxygen atom without the H attached.
• In the Lewis structure for HNO₃ there are a total of 24 valence electrons.

Transcript: This is the HNO3 Lewis structure. For HNO3, nitric acid, we have a total of 24 valence electrons. So when you have a structure like nitric acid where you have the H and then the NO3, the Oxygens there at the end, think of it as drawing the NO3 structure and then putting that H on one of the Oxygens. So that's with these acids that we're talking about here. So let's try that: we'll put an N, three Oxygens, and we'll put the H right here. So let's put valence electrons between atoms to form chemical bonds. So there we go.

And then we'll put them around the Oxygens here to make sure each one of those has eight. And then 24 goes right there. So we've used all 24 valence electrons. All of the Oxygens have 8. The Hydrogen here, it has 2, and that's all it needs. But the Nitrogen in the center only has 6. So we'll take and move these two valence electrons to form a double bond. By doing that, Nitrogen now has 8; this Oxygen right here, it has 8; and we've still used only 24 valence electrons.

When we calculate our formal charges, this Oxygen up here will have a negative 1 and the Nitrogen will have a positive 1. Everything else will be zero. So that looks pretty reasonable—it adds up to 0 here. One question you might ask is, why didn't we put a double bond right here on this Oxygen instead of putting it over here? Because that would work, too, in terms of octets. So over here, now the double bond is between the Nitrogen connected to the OH. Where over here, the double bond is just the Oxygen and the Nitrogen. Notice the difference in formal charges. Over here you have a +1 on the Nitrogen and then a -1 on the Oxygen. That makes sense; Oxygen's more electronegative, so it should have th negative. Over here, you have a +1 on the Nitrogen and then you have a -1 on the Oxygen, a -1, and then a +1 on this Oxygen. That doesn't really make sense for an Oxygen to have a +1: it's more electronegative.

So the best structure is going to be this one right here, where the formal charges are closer to 0 and they make sense. In both cases, they add up to a total charge of 0 for the molecule.

This is Dr. B. with the Lewis structure for HNO3: nitric acid. Thanks for watching.