What property of lithium makes them forms the nitride, lithium nitride $\ce{Li3N}$ whereas the other group 1 elements forms the azide, like sodium azide and potassium azide - $\ce{NaN3}$ and $\ce{KN3}$ respectively?

Does lithium azide exist? If so, what is its structure?

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    $\begingroup$ This is an example where the application of HSAB is appropriate. Consider that the hardness of the metal cations of the alkali metals increases down the group. Also, consider that azide is a softer base compared to nitride. However, this explains it only qualitatively... $\endgroup$ Aug 18, 2018 at 8:52

1 Answer 1


The formation of $\ce{Li3N}$ can be explained thermodynamically. The enthalpy of formation of the $\ce{N^3-}$ ion is extremely endothermic (it involves three successive additions of electrons) and with the larger counterions $\ce{Na+}$ or $\ce{K+}$ the lattice energy (which is proportional to $\frac{q_+ q_-}{r_+ + r_-}$) is not sufficiently large to compensate for the large $\Delta_\text{f}H$ of $\ce{N^3-}$. The same argument explains why magnesium also forms a nitride.

According to my very brief research on the Internet, lithium azide does exist but is unstable. It can be prepared via reaction of $\ce{NaN3}$ and $\ce{Li2SO4}$: see Acta Chem. Scand. 1957, 11, 581 for more details.

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    $\begingroup$ I’m pretty sure that sodium nitride will exist, too, won’t it? $\endgroup$
    – Jan
    Oct 17, 2016 at 23:59
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    $\begingroup$ @Jan Wikipedia says it exists, but is unstable and readily decomposes into $\ce{Na + N2}$ - no surprises there. $\endgroup$ Oct 22, 2016 at 14:37

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