Azide is the anion with the formula N−3. It is the conjugate base of hydrazoic acid (HN3). N−3 is a linear anion that is isoelectronic with CO2, NCO−, N2O, NO+2 and NCF. Per valence bond theory, azide can be described by several resonance structures; an important one being . Azide is also a functional group in organic chemistry, RN3.