difference between linear and bent, or v-shape

[George_Zhu]

why I3^-1 is a linear but not a bent or V shape?

[Chem_Mod]

Based on VSEPR geometries, if the central atom has three pairs of electrons, the molecule is linear (it must also have two noncentral atoms). The formal charge of I (central atom) is -1 so that is where the charge comes from in I3^-1. I can break the octet rule and hold more electrons since it has d orbitals. Because the formal charges of the noncentral atoms are already zero, it makes the most sense to add the extra lone pair to the central atom.