## Chemistry: The Central Science (13th Edition)

$ScI_{3}$
When a compound is formed, the overall charge must be neutral. Scandium, the problem states, has a charge of +3. Iodine ions will seek the electron configuration of the nearest noble gas, in this case Xenon. Because Iodine must gain an electron to get this electron configuration, Iodine ions will have a charge of -1. Thus, there must be three Iodine ions to gain an overall charge of -3, which will cancel out the +3 charge of Scandium, making the compound $ScI_{3}$.