Here's why:

* Cesium is an alkali metal, meaning it has one valence electron and readily loses it to form a +1 cation (Cs+).

* Sulfur is a nonmetal in group 16, meaning it has six valence electrons and tends to gain two electrons to form a -2 anion (S²⁻).

The strong electrostatic attraction between the positively charged cesium cation and the negatively charged sulfide anion results in the formation of an ionic bond.

The resulting compound would be cesium sulfide (Cs₂S).