in group1,only Li react wif N?

Li3N is the only nitride of the Group I metals. In other words, Na3N, K3N, Rb3N and Cs3N do NOT exist.
Li3N 是唯一的第 I 族金屬的氮化物。換句話說，Na3N、K3N、Rb3N 和 Cs3N 並不存在。

Group I metals form M⁺ ion, while nitrogen form N³¯ ion. Therefore, the general formula of the nitride of a Group I metal is M3N. Each mole of M3N contains 3 moles of M⁺ ions and 1 mole of N³¯ ions. The number of M⁺ ions is tripled that of N³¯ ions.
第 I 族金屬形成 M⁺ 離子, 而氮形成 N³¯ 離子。因此，第 I 族金屬的氮化物，其通式是 M3N。每莫耳的 M3N 含有 3 莫耳的 M⁺ 和 1 莫耳的 N³¯ 離子，M⁺ 離子的數目是 N³¯ 離子數目的3 倍。

Li⁺ ions are small enough to form a stable lattice of Li3N, but other cations of the Group I metals is NOT. This is because Li⁺ ions are smaller enough to prevent themselves from touching each other in the lattice, but other cations of the Group I metals would touch each other due to their large size.
Li⁺ 離子足夠細小去形成穩定的 Li3N 晶格，但其他第 I 族金屬的陽離子則不能。因為 Li⁺ 足夠細小去避免它們本身之間在晶格中互相接觸，但其他第 I 族金屬陽離子會因為其較大體積而在晶格中互相接觸。