Elemental nitrogen occurs as a very stable diatomic molecule. Only two naturally occurring isotopes
are found, 14 N (99.635%) and 15 N. The occurrence mainly as 14 N is somewhat unusual in view of the
fact that so few odd-odd nuclei are stable. Nitrogen molecules are small, having a bond length of only
110 pm (1.10 Å) owing to the strong triple bond holding the atoms together (945 kJ/mol). This very
strong and stable bond (the force constant is 22.4 mdyn Å 1 ) is partially responsible for the explosive
nature of some nitrogen compounds. The molecular orbital diagram for N 2 , shown in Figure 14.3 ,
indicates that the bond order is 3 in this extremely stable molecule.