This is the OCN- Lewis structure: the cyanate
Ion. for the cyanate ion, we have a total
of 16 valence electrons. That includes this
negative up here. Carbon is the least electronegative;
we'll put that at the center. Then an Oxygen
here, and a Nitrogen over here. We'll put
2 electrons between atoms to form a chemical
bond. Then we'll go around the outside, so
we have 2, 4, 6, 8, 10, 12, 14, 16. We've
used all our valence electrons at this point.
Oxygen and Nitrogen have 8 valence electrons,
so they're good. But the Carbon only has 4.
We're going to need to share valence electrons
from the outer atoms with the Carbon so it
can have an octet. The question is, do we
share from the Oxygen or from the Nitrogen
or both? Nitrogen is less electronegative
than Oxygen. That means it's more likely to
give up valence electrons, to share them.
So let's move them from the Nitrogen. So let's
take 2 from here and form a double bond. Now
the Carbon has 6, so we need to move 2 more.
Let's put those in there. So now Nitrogen,
it has 8, but the Carbon also has 8. We're
still only using 16 valence electrons. When
we calculate the formal charges, we'll find
that the Oxygen has a formal charge of -1,
Carbon is 0, and Nitrogen is 0. That makes
a lot of sense: we have a -1 up here. The
negative charge in our OCN- Lewis structure
is on the most electronegative atom. So this
looks like a pretty good Lewis structure.
We could form double bonds between the Oxygen
and then between the Carbon and Nitrogen.
You'd see that that would work from an octet
standpoint, but when we check our formal charges,
we'd have a -1 on the Nitrogen. That doesn't
make sense, because Nitrogen is less electronegative.
So this right here is the best Lewis structure
for OCN-. I'm Dr. B., and thanks for watching.
