Whenever I want to draw the Lewis structure,

the first I need to find out is the number of valence electrons in the molecule.

Here I have three iodine atoms, each with 7 electrons

plus 1 additional electrons from the minus charge for a total of 22 electrons.

So when I look at the Lewis structure of this molecule.

I'm first going to draw this, with all single bonds, so

we have our skeletal structure.

I've used up 4 electrons, I have 18 electrons remaining.

I'm going to fill in, the electrons on the terminal atoms first, so

that now I have 16 electrons used.

I have 22 total, so I've got 6 more to go.

And therefore I'm going to put the remaining 6 on that central atom, Iodine.

I'm also going to show this in brackets with a minus sign,

just to indicate that this is a charged species.

Now I've used my 22 electrons.

Notice that Iodine does have an expanded octet, it has 10 electrons around it.

Iodine is beyond the second period, and so that's perfectly fine for that structure.