Nitrogen is a non-metal, with an electronegativity of 3.0. It has five electrons in its outer shell, so is trivalent in most compounds. Pure nitrogen is an unreactive colorless diatomic gas at room temperature, and comprises about 2/3 of the Earth's atmosphere. It condenses at 77 K and freezes at 63 K. Liquid nitrogen is a common cryogen.
The main hydride of nitrogen is ammonia (NH3) although hydrazine (N2H4) is also well known. Ammonia is somewhat more basic than water, and in solution forms ammonium ions (NH4+). Liquid ammonia in fact slightly amphiprotic and forms ammonium and amide ions (NH2-); both amides and nitride (N3-) salts are known, but decompose in water.
Another kind of nitrogen anions are azides (N3-), which are linear and isoelectronic to carbon dioxide. Another molecule of the same structure is dinitrogen monoxide (N2O), or laughing gas. This is one of a variety of oxides, the most prominent of which are nitrogen monoxide (NO) and nitrogen dioxide (NO2), which both contain an unpaired electron. The latter shows some tendency to dimerize and is an important component of smog.
The more standard oxides, dinitrogen trioxide (N2O3) and dinitrogen pentoxide (N2O5), are actually fairly unstable and explosive. The corresponding acids are nitrous (HNO2) and nitric acid (HNO3), with the corresponding salts called nitrites and nitrates. Nitric acid is one of the few acids stronger than hydronium and its salts including some important minerals, like salt peter.