Introduction to Nitrogen Chemistry

Nitrogen has electronic configuration [He]2s²2p³, and accessible oxidation states from -3 to +5. It has more valence electrons than orbitals (2x2s and 3x2p = 5, in 4 orbitals), so lone pairs play an important role in its chemistry.

N₂ is inert; the very strong N-N triple bond is very stable towards decomposition and reaction, and this means that nitrogen gas is often used to make an inert atmosphere for the handling of and manufacture of oxygen sensitive compounds.

The N-N single bond is, however, weak; all N-X bonds are weak, with the exception of N-H, due to the presence of the strong electrostatic repulsion between non-bonded electrons on the adjacent atoms (an example of the influence of the lone pair on N). N therefore has a tendency to form strong, multiple bonds, such as N=O, N=S, N=C, and the triple bonds in N₂ and -CN (the cyanide group), and many N containing compounds are unstable with respect to the formation of N₂. (For a comparison between the chemistries of nitrogen and phosphorous, click here.)

N₂ bonds to metals in a synergic bonding process in much the same way as Carbon Monoxide (CO), with which it is isoelectronic. Here, there is donation of the N lone pair electrons to form a M-N σ-bond, and then back donation of electrons from the metal into the antibonding π^*-orbitals on the N.

The above reaction may give some indication of the kind of process happening in the fixation of N₂ in soils (the catalytic conversion to NH₄⁺ by the enzyme nitrogenase). A similar reaction in the tungsten compound yields NH₄⁺ from the N₂ containing reactant.

Occurrence

Nitrogen occurs mainly as N_{2 (g)} (~79% of the atmosphere) and is obtained by the distillation of liquid air.

Nitrides

These are often difficult to classify. The N^3- ion is highly charged and so is is only stabilized by small, highly polarizing cations, such as Li⁺ and Mg²⁺, and formulation of N as N^3- might not be correct. In Li₃N, it is better to think of the compound as (Li₂N)^–Li⁺, as demonstrated by the layer structure.