Azide
Azide is the anion with the formula N3. It is the conjugate base of hydrazoic acid (HN3). N3 is a linear anion that is isoelectronic with CO2 and N2O. Per valence bond theory, azide can be described by several resonance structures, an important one being N=N=N. Azide is also a functional group in organic chemistry, RN3. The dominant application of azides is as a propellant in air bags.