The formula of the compound formed between Lithium (Li) and Sulfur (S) is Li₂S. Here's why:

* Lithium is in Group 1 of the periodic table, meaning it has a +1 charge as a cation (Li⁺).

* Sulfur is in Group 16 of the periodic table, meaning it has a -2 charge as an anion (S²⁻).

To form a neutral compound, you need two lithium ions (2 x +1 = +2) to balance the charge of one sulfide ion (-2).