Drawing the Lewis Structure for ClO3-

Viewing Notes:

  • The Lewis structure for ClO3- requires you to place Chlorine (Cl) in the center of the structure since it is the most electronegative.
  • You might think you've got the correct Lewis structure for ClO3- at first. Remember, Chlorine is in Period 3 and can hold more than 8 valence electrons.
  • You'll want to calculate the formal charges on each atom to make sure you have the best Lewis structure for ClO3-.
  • There are a total of 26 valence electrons for ClO3-.
  • Remember to put brackets around the Lewis structure, along with a negative sign, to show that it is an ion.

Transcript: Let's do the ClO3- Lewis structure. Chlorine has 7 valence electrons; plus 6 for Oxygen, times 3; and this up here means we have another valence electron for a total of 26 valence electrons. Chlorine is the least electronegative, that goes in the center. Oxygens around it. Two valence electrons to form chemical bonds between the atoms. We've used 6. And then around the outside atoms, 8, 10, 24; we have 2 left over there, we'll put them down here to complete the octet for Chlorine. So we've used all 26 valence electrons, and each of the atoms now has an octet.

So it looks pretty good, except Chlorine is in period 3 of the periodic table. That means that it can often hold more than 8 valence electrons, so we need to check our formal charges. Turns out our formal charges show that we have a +2 formal charge on the Chlorine and that the Oxygens each have a -1 formal charge. If you add that all up it does give you a -1 formal charge, which makes sense, but the closer the formal charges are to zero, the better the structure is.

Let's take a look and see how we can fix this. If I take these valence electrons right here and move them into the center for two Oxygens, that should take care of this +2 charge. So let's see what that does to our formal charges now that we've moved those in there to form a double bond. So by making those double bonds between this Oxygen and Chlorine and this one here, we now have a formal charge of zero on the Chlorine, and on these two Oxygens right here; while this Oxygen, the black one, has a -1 charge. That makes sense because the total charge here: negative 1, and this is negative 1 as well. One last thing: since it is an ion, we do need to put brackets around it to show that it is an and it has a negative charge.

And that represents the best structure for ClO3-. I'm Dr. B., and thanks for watching.