Fluorine is a highly electronegative element, meaning that it has a strong tendency to attract electrons. Rubidium is a highly electropositive element, meaning that it has a strong tendency to lose electrons. When these two elements come into contact, the fluorine atoms will take electrons from the rubidium atoms, resulting in the formation of positively charged rubidium ions and negatively charged fluoride ions. These ions will then combine to form an ionic compound, rubidium fluoride (RbF).