Magnesium (Mg) belongs to group II A in the periodic table with atomic number = 12
Mg Electron configuration = 1s²2S²2p⁶3s²
Nitrogen (N) belongs to group V A in the periodic table with atomic number = 7
N electron configuration= 1s²2s²2p³
Valence electrons for Mg = 2
Valence electrons for N = 5
Mg loses 2 electrons and N gains 3 electrons to complete its octet
Thus, the Formula unit when Mg and N bond is Mg₃N₂