Because of their high reactivity, they must be stored under oil to prevent reaction with air, and are found naturally only in salts and never as the free elements.
bɪkˈʌz ʌv ðɛɹ hˈaɪ ɹɪɐktˈɪvᵻɾi, ðeɪ mˈʌst biː stˈoːɹd ˌʌndɚɹ ˈɔɪl tə pɹɪvˈɛnt ɹɪˈækʃən wɪð ˈɛɹ, ænd ɑːɹ fˈaʊnd nˈætʃɚɹəli ˈoʊnli ɪn sˈɔlts ænd nˈɛvɚɹ æz ðə fɹˈiː ˈɛlɪmənts.