Lewis Structure for I3-

[Melody Zhang 3L]

Iodine has 7 valence electrons, so at first, I allocated 3 lone pairs around each of the Iodines, with the central iodine having a formal charge of -1. However, I realized that I was taught to place the negative charge on the outside atoms whenever possible, so I made one of the lone pairs of the central iodine atom into a double bond, so that the formal charge was -1 on one of the outside atoms. This changed the shape of the molecule to be bent instead of linear. The actual molecule was the structure that I originally thought, and is linear. Can someone explain why?

[Jeremy_Guiman2E]

This seems to be the correct electron dot diagram:



The outer I's have a formal charge of 0, and I believe the formal charge of -1 is ok on the central I atom because of the fact that I₃^- is a negatively charged molecule, with an overall charge of -1.