Here's why:

* Lithium (Li) is in Group 1 of the periodic table, making it a +1 cation (Li⁺).

* Iodine (I) is in Group 17 of the periodic table, making it a -1 anion (I⁻).

To form a neutral compound, one lithium ion (Li⁺) combines with one iodide ion (I⁻).