Question

answer the questions in the table below about the shape of the triiodide (i₃⁻) anion.
how many electron groups are around the central iodine atom?
note: one \electron group\ means one lone pair, one single bond, one double bond, or one triple bond.
what phrase best describes the arrangement of these electron groups around the central iodine atom? (you may need to use the scrollbar to see all the choices.)

Explanation:

Step1: Determine electron - group count

The central iodine atom in $I_3^-$ has 2 bonding pairs (to the two terminal iodine atoms) and 3 lone pairs. So the total number of electron - groups is $2 + 3=5$.

Step2: Identify electron - group arrangement

Based on VSEPR (Valence - Shell Electron - Pair Repulsion) theory, when there are 5 electron - groups around a central atom, the electron - group arrangement is trigonal bipyramidal.

Answer:

How many electron groups are around the central iodine atom? 5
What phrase best describes the arrangement of these electron groups around the central iodine atom? Trigonal bipyramidal