Nitrogen exists in its elemental form as
Nitrogen – Nitrogen triple bond in N2 molecule has very high thermodynamic stability. It has a dissociation energy of 942 kJ.mol−1
This makes nitrogen exist as a diatomic gas at room temperature. Also, this increased stability of the N≡N makes it non-polar and hence the Van der Waals forces between the molecules are low. This is the reason why Nitrogen is a gas at room temperature. These reasons also make N2 molecule pretty inert at ordinary temperatures and pressure(s).