Drawing the Lewis Structure for I3-
Transcript: This is Dr. B. Let's do the I3- Lewis structure. On the periodic table, Iodine is in group 7 or 17. It has seven valence electrons. But we have three of them (Iodine atoms). And then we have this negative up here. So we're going to add another electron to that: so 21 plus 1, 22 total valence electrons so will put our Iodines in lines like this and then we're gonna put electrons between each of the atoms to form chemical bonds. Put a pair here, here, here and now around atoms. So we used 2, 4, 6, 8, 10, 12, 14, 16, so we have six left over and we'll just have to put them on the Iodine right here like this. so we've used all 22 of the valence electrons that we had available and it's kind of strange structure so let's check or formal charges just to make sure that we have the best Lewis Structure for I3-.
So the two Iodines on the outside, the ones in green, let's do those first. They're the same so they'll have the same formal charge. On the periodic table Iodine is in group seven; seven valence electrons. Non-bonding, these right here that are not involved in chemical bonds, we have six and then bonding we have two but we'll divide that by two. Seven minus six minus one gives us zero. For the Iodine in the middle, the blue Iodine, seven valence electrons for iodine we have six non-bonding, so these four up here aren't bonding and these two down here so six non-bonding valence electrons and then we have two plus two, four bonding valence electrons which will divide by two. Seven minus six minus two gives us a negative one charge.
So all of this makes sense. We have the negative one charge here. That makes sense: we have a negative three so we can draw this with brackets so everyone can see that it is an ion. Put a negative up there.
That's the Lewis structure for I3-. This is Dr. B, and thanks for watching.