The alkalides are an exception: they are unstable compounds which contain alkali metals in a −1 oxidation state, which is very unusual as before the discovery of the alkalides, the alkali metals were not expected to be able to form anions and were thought to be able to appear in salts only as cations.
ðɪ ˈælkəlˌaɪdz ɑːɹ ɐn ɛksˈɛpʃən: ðeɪ ɑːɹ ʌnstˈeɪbəl kˈɑːmpaʊndz wˌɪtʃ kəntˈeɪn ˈælkəlˌaɪ mˈɛɾəlz ɪn ɐ mˈaɪnəs wˈʌn ˌɑːksɪdˈeɪʃən stˈeɪt, wˌɪtʃ ɪz vˈɛɹi ʌnjˈuːʒuːəl æz bᵻfˌoːɹ ðə dɪskˈʌvɚɹi ʌvðɪ ˈælkəlˌaɪdz, ðɪ ˈælkəlˌaɪ mˈɛɾəlz wɜː nˌɑːt ɛkspˈɛktᵻd təbi ˈeɪbəl tə fˈɔːɹm ˈænaɪənz ænd wɜː θˈɔːt təbi ˈeɪbəl tʊ ɐpˈɪɹ ɪn sˈɔlts ˈoʊnli æz kˈæɾaɪənz.