The lattice energy is maximised with small, highly charged ions; the alkali metals do not form highly charged ions, only forming ions with a charge of +1, so only lithium, the smallest alkali metal, can release enough lattice energy to make the reaction with nitrogen exothermic, forming lithium nitride.
ðə lˈæɾɪs ˈɛnɚdʒi ɪz mˈæksɪmˌaɪzd wɪð smˈɔːl, hˈaɪli tʃˈɑːɹdʒd ˈaɪɑːnz; ðɪ ˈælkəlˌaɪ mˈɛɾəlz duːnˌɑːt fˈɔːɹm hˈaɪli tʃˈɑːɹdʒd ˈaɪɑːnz, ˈoʊnli fˈɔːɹmɪŋ ˈaɪɑːnz wɪð ɐ tʃˈɑːɹdʒ ʌv plˈʌs wˈʌn, sˌoʊ ˈoʊnli lˈɪθiəm, ðə smˈɔːlɪst ˈælkəlˌaɪ mˈɛɾəl, kæn ɹᵻlˈiːs ɪnˈʌf lˈæɾɪs ˈɛnɚdʒi tə mˌeɪk ðə ɹɪˈækʃən wɪð nˈaɪtɹədʒən ɛɡzəðˈɜːmɪk, fˈɔːɹmɪŋ lˈɪθiəm nˈaɪtɹaɪd.