## Confusion on Homework Problem 4.13 Part A

(Polar molecules, Non-polar molecules, etc.)

Katie Clark 3B
Posts: 26
Joined: Fri Sep 25, 2015 3:00 am

### Confusion on Homework Problem 4.13 Part A

I am confused as to why the shape of the molecule I3- is linear. I got the correct Lewis structure for the molecule. The central atom had five regions of electron density. Why then is the shape linear? Wouldn't the three lone pairs of electrons affect the shape? Could someone please explain this to me? Thanks!

YeChan Lee
Posts: 14
Joined: Fri Sep 25, 2015 3:00 am

### Re: Confusion on Homework Problem 4.13 Part A

Hey there,

So I guessed you're confused about the shape of the molecule. Well if you remember it from your lecture, 5 pairs of valence electrons forms a trigonal bipyramidal shape. Just think of it as two pyramids stuck together. Now this shape can be also viewed as a linear line as its y axis and a triangle as its x axis. For I3-, you have 3 lone pairs and 2 bonds. You're basically taking off three points from the structure. The atoms try to even themselves out. So the triangle from the x axis disappears and only the y axis linear line is left. I'm so sorry if you didn't understand what I'm writing. The shape is very hard to describe in words.
But tl;dr, 5 pairs = trigonal bipyramidal, but with only 2 bonds = linear.