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This is the NO3- Lewis structure: the nitrate ion. Nitrogen has 5 valence electrons. Oxygen
has 6, we have 3 Oxygens, and we need to add 1 for this valence electron up here. That
gives us a total of 5 plus 18 plus 1: 24 valence electrons. Nitrogen is the least electronegative;
we'll put that in the center, and we'll put the Oxygens--all three of them--on the outside.
We'll put two valence electrons between the atoms to form chemical bonds. So we've used
six; we'll go around the outside: 8, 10, and 24 valence electrons. We can see that each
of the Oxygens has 8 valence electrons, so its octet is fulfilled. But the Nitrogen only
has 6 valence electrons. We can take 2 electrons from one of the Oxygens on the outside and
move it between the Nitrogen and Oxygen to form a double bond. When we do that, this
Oxygen right here still has 8 valence electrons, but the Nitrogen now has 8. So we have fulfilled
the octets on all of the atoms in the Lewis structure for NO3-. At the same time, we've
only used 24 valence electrons. If you calculate the formal charges, you'll see that the Nitrogen
has a +1 formal charge. These two Oxygens with the single bond have a -1, while the
double bonded Oxygen has a formal charge of zero. If we add all these up, we'll find out
that it equals -1, which makes a lot of sense because we have a negative on the NO3- ion.
One more thing we need to do for the NO3- Lewis structure is put brackets around the
structure to show that it is an ion and it has a negative charge. So that's the Lewis
structure for NO3-, the nitrate ion. This is Dr. B., and thanks for watching.