Quick question: which elemental metal will spontaneously react with N2 at 1 atm and about 298 K to give a stable crystalline nitride, and what specific thermodynamic factor makes this favorable while its heavier congeners don’t? I once watched a freshly cut sample develop a dark red surface within about 3 minutes in a glovebox N2 stream.
Lithium — the maroon Li3N forms at room temp in dry N2, driven by the unusually high lattice enthalpy of Li3N (small Li+ stabilizing N3−), so ΔG is favorable while Na/K aren’t. Scratch and re-expose a fresh Li cut under N2 and you should see the red bloom within minutes; was your box at sub‑ppm O2/H2O? Li’s the group overachiever on this one: Lithium nitride - Wikipedia.