HW 4.13

[Shimran Kumar 1C]

The problem asks for the molecular shape of I₃^-. The Lewis structure shows 3 lone pairs and 2 bonding pairs around the central Iodine. The solutions manual states the shape is linear.

Why would the shape be linear if there is an odd number of lone pairs pushing on the atoms? I thought the molecule would be bent.

[Jack Martinyan 1L]

When you draw the Lewis structure of the I3- ion, you end up with two iodines attached to a central iodine. The central iodine also has three lone pairs on it. This gives you 5 regions of electron density around the central atom. This gives a trigonal bipyramidal shape. The electron pairs repel each other, so they want to maximize their distance from one another, so they take up equatorial positions 120 degrees from one another, and the two other iodines are 180 from one another. Thus the overall shape is linear.



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[Shimran Kumar 1C]

That actually makes perfect sense! Thank you so much!