Lewis Dot of the Triiodide Ion
I does not follow the octet rule. It will hold more than 8 electrons.
Iodine having valence electrons in the 4th energy level, will also have access to the 4d sublevel, thus allowing for more than 8 electrons. I3- is dsp3 hybridized and contains 3 lone pairs and 2 bonding pairs of valence electrons around the Iodine. The VSEPR predicts the linear shape.
Elements in the first 2 periods of the Periodic Table do not have access to the d sublevel and must adhere to the octet (or duet H and He) rule.