This is unusual as periodic trends, ignoring relativistic effects would predict ununennium to be even more reactive than caesium and francium.
ðɪs ɪz ʌnjˈuːʒuːəl æz pˌiəɹɪˈɑːdɪk tɹˈɛndz, ɪɡnˈoːɹɪŋ ɹˌɛləɾɪvˈɪstɪk ɪfˈɛkts wʊd pɹɪdˈɪkt ʌnˌʌnɛnˈɪəm təbi ˈiːvən mˈoːɹ ɹɪˈæktɪv ðɐn sˈiːsiəm ænd fɹˈænsiəm.