Here's why:

* Electron configuration: Caesium has an electron configuration of [Xe] 6s¹. This means it has one electron in its outermost shell.

* Tendency to lose electrons: Caesium, being an alkali metal, readily loses this single electron to achieve a stable octet configuration. This results in a +1 charge.

Therefore, caesium forms ionic compounds where it exists as the Cs⁺ ion.