Question

answer the questions in the table below about the shape of the triiodide (i₃⁻) anion.
what word or two - word phrase best describes the shape of the i₃⁻ anion?
what is the angle between the iodine - iodine bonds? (if there is more than one angle, pick the smallest.)

Explanation:

For the first question (shape of $\boldsymbol{I_3^-}$ anion):

To determine the shape of $I_3^-$, we use VSEPR theory. The central iodine atom has 7 valence electrons, plus 1 from the negative charge, and 2 bonds (each contributing 2 electrons, but in VSEPR, we consider bonding and non - bonding electron pairs). The central I has 3 lone pairs and 2 bonding pairs (to the two terminal I atoms). The electron - pair geometry is trigonal bipyramidal, but with 3 lone pairs in the equatorial positions, the molecular geometry (shape) is linear.

In a linear molecular geometry, the bond angle between the two iodine - iodine bonds is 180 degrees. Since the shape is linear, the angle between the bonds (the smallest, and in this case the only relevant angle) is 180°.

Answer:

linear

For the second question (bond angle in $\boldsymbol{I_3^-}$):