* Electronegativity Difference: Rubidium (Rb) is a metal with a low electronegativity, while Fluorine (F) is a highly electronegative nonmetal. The difference in electronegativity between them is significant, leading to the transfer of an electron from Rubidium to Fluorine.

* Formation of Ions: Rubidium loses one electron to become a positively charged ion (Rb+), while Fluorine gains one electron to become a negatively charged ion (F-).

* Electrostatic Attraction: The oppositely charged ions attract each other strongly, forming an ionic bond.

In summary: The large electronegativity difference between Rubidium and Fluorine results in the formation of ions and their electrostatic attraction, characteristic of an ionic bond.