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.
