No attempts at synthesis have been made for any heavier alkali metals: due to their extremely high atomic number, they would require new, more powerful methods and technology to make.
nˈoʊ ɐtˈɛmpts æt sˈɪnθəsˌɪs hɐvbɪn mˌeɪd fɔːɹ ˌɛni hˈɛviɚɹ ˈælkəlˌaɪ mˈɛɾəlz: dˈuː tə ðɛɹ ɛkstɹˈiːmli hˈaɪ ɐtˈɑːmɪk nˈʌmbɚ, ðeɪ wʊd ɹᵻkwˈaɪɚ nˈuː, mˈoːɹ pˈaʊɚfəl mˈɛθədz ænd tɛknˈɑːlədʒi tə mˈeɪk.