Name: Worked example: Lewis diagram of the cyanide ion (CN⁻) | AP Chemistry | Khan Academy
Uploaded: 2020-03-27T17:40:53.000Z
Duration: 4 min 28 s
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- [Instructor] In this video we're gonna try to get

more practice constructing Lewis diagrams.

And we're gonna try to do that for a cyanide anion.

This is the first time we're constructing

So pause this video and see if you can have a go at that.

the total valence electrons that we're dealing with.

And the reason why we do that is to make sure

that we're allocating all the valence electrons.

we can look at a periodic table of elements.

in that second shell, it's in the second period,

so you have four valence electrons from carbon.

Nitrogen has one, two, three, four, five valence electrons

in its second shell, it's in that second period.

And so the valence electrons from a neutral carbon

would be a total of nine valence electrons.

It is an anion, it has a negative one charge.

we can think about it having an extra valence electron.

So we're dealing with a total of 10 valence electrons.

Now, the next step is to try to draw single bonds.

Try single bonds, and identify a central atom.

I have now accounted for two valence electrons.

So now I am left with eight valence electrons,

So let me start with the more electronegative.

of these remaining valence electrons, six, so minus six,

So let me give carbon two valence electrons, like that.

Nitrogen has eight valence electrons hanging around,

whether we would want to have some extra bonds,

So how can we give carbon more valence electrons?

we could take some of these lone pairs around nitrogen

and then use them, turn this single covalent bond

So let's see, if we were to take these two

and then I'll just draw another covalent bond.

So nitrogen still has eight electrons hanging around.

and make another covalent bond out of them.

So let me make a covalent bond out of them.

We still haven't represented this negative charge

The way that we would do that is say hey,

this entire molecule, you put brackets around it,

We've allocated all of our valence electrons,

we have our octet rule on all of our atoms

that are not hydrogen, there's no hydrogen here,

and we're showing that this indeed is an anion,

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Worked example: Lewis diagram of the cyanide ion (CN⁻) | AP Chemistry | Khan Academy

entire

essentially

period

practice