cannot make long chains in the way that carbon can, for two reasons.
The lone electron pairs on adjacent nitrogen atoms in a -N-N-N-N-
chain repel one another more strongly than bonding pairs in the C-H
bonds of hydrocarbons do. This weakens the N-N bond and makes it only
half as strong as a C-C bond. The second factor is the great stability
of the pieces of the ruptured chain, N2
molecules. Nitrogen has three unpaired electrons for bonding,
and it can share all three with a neighboring atom to produce the
NN molecule shown at the right. Pure nitrogen therefore is a diatomic
, similar to H2.
Because the triple bond is quite strong, N2
is a stable and relatively unreactive molecule. If "quadruple
bonds" were possible, with four electron pairs shared between two
atoms, then perhaps carbon also would be a diatomic gas, C2
. But this is not possible, so carbon bonds to more than one
neighbor and forms the three-dimensional structures of graphite and
diamond. The sudden change in properties between solid diamond and
gaseous nitrogen is one of the most dramatic among the chemical elements.