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.
Nitrogen occurs mainly as N2 (g) (~79% of the atmosphere) and is obtained by the distillation of liquid air.
These are often difficult to classify. The N3- 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 N3- might not be correct. In Li3N, it is better to think of the compound as (Li2N)–Li+, as demonstrated by the layer structure.
Structure of Li3N
|Layered structure consisting of hexagons of Li+ ions with N3- at the centers (Li2N)–, with Li+ ions bridging the layers, sited between two N ions.|