Chemical Bonding: N₂O₅ Lewis Structure

Drawing the Lewis Structure for N₂O₅

Viewing Notes:

• There are a total of 40 valence electrons in the N₂O₅ Lewis structure.
• N₂O₅ is a bit tough - it will take some trial and error to find the best structure. They key is placing an Oxygen (O) atom between the two Nitrogen atoms. Then you can attach the other four oxygen atoms to the Nitroge atoms.
• Nitrogen (N) is the least electronegative atom and goes at the center of the N₂O₅ Lewis structure. But remember, for this structure you'll need to put an Oxygen (O) atom between Nitrogen (N) atoms. This is an exception to our "least electronegative atom at the center rule". That's what makes the N₂O₅ Lewis structure tricky.
• With N₂O₅ you'll should check the formal charges to see if this structure makes sense.

Transcript: OK, the Lewis structure for N2O5 is a bit challenging. If you had time, you could work to fill the octets and find a combination where they all were satisfied, and you could look at the formal charges and make sure they were all as close to zero as possible. But let me start you out with a skeleton structure, and we'll work from there just to save some time. So that's the skeleton structure for N2O5, and we have a total of 40 valence electrons to work with. First, we'll 2 between atoms to form chemical bonds--we've used 12 valence electrons--and then we'll go around the outside and fill the atoms until we've satisfied their octets or we've run out of valence electrons. So that's 36 valence electrons.

We'll move to the center; 38 and then 40. You can see the octets are fulfilled for all the atoms except this central Oxygen which only has 4 valence electrons. We could take these two electrons and share them, do the same over here, and that would give us an octet on this central Oxygen and we'd still only be using 40 valence electrons.

The problem is, when we look at our formal charges, they don't seem quite right. First of all, they're not very close to 0. And then when I look at this central Oxygen here, Oxygen's more electronegative than the Nitrogens here. I wouldn't expect to see a positive 2 formal charge on an Oxygen. So I don't think this is the best structure for N2O5. Let's go back and see if we can do something different. First, I think I'll move these valence electrons here onto the central Oxygen. That'll give it a formal charge of 0.

The problem is, now my Nitrogens only have 6 valence electrons. I can move the valence electrons from the Oxygen here to share, create a double bond, that should solve that problem. And that'll also reduce the formal charge on these Oxygens here. So now, if I look at my formal charges, they're a lot closer to 0 and the +1 is on the Nitrogrens. That makes sense because Nitrogen is a little bit less electronegative than Oxygen. And the Oxygens have the negative 1's.

So this is probably the best we're going to be able to do here. We've fulfilled the octets on all of the atoms and our formal chages are pretty close to 0. The positive charges are on the least electronegative atoms--that makes sense, as well.

So this is the Lewis structure for N2O5. This is Dr. B., and thanks for watching.