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Nitrogen accounts for 78.1 % of Earth's atmosphere. Despite its inertness—so much so that Lavoisier dubbed it “azote,” meaning “without life”—it is indispensable to life and industry, forming the backbone of DNA, agricultural fertilizers, and numerous industrial processes.
Nitrogen gas (N₂) is a nonmetallic, colorless, odorless, and tasteless diatomic molecule. With an atomic number of 7 and an atomic weight of 14.0067, it has a density of 1.251 g L⁻¹ at 0 °C and a specific gravity of 0.96737, slightly lighter than air. Its triple point—where gas, liquid, and solid coexist—occurs at –210 °C (63 K) and 12.6 kPa.
Below its boiling point of –195.79 °C (77 K), nitrogen condenses into liquid nitrogen, a clear, odorless fluid that resembles water. Cooling further to its melting point of –210 °C (63 K) yields a fluffy, snow‑like solid.
In most compounds, nitrogen forms trivalent covalent bonds. The N₂ molecule contains a remarkably strong triple bond, supported by five valence electrons and an electronegativity of 3.04 (Pauling scale), which underpins its chemical stability.
The abundance and chemical inertness of nitrogen make it invaluable in industry. It is used in food preservation and fire‑suppression systems, protects oxygen‑sensitive materials such as iron, steel, and electronics during manufacturing, and serves as a key feedstock for ammonia synthesis via the Haber–Bosch process.
In 2001, a study published in Nature reported that researchers at the Carnegie Institution of Washington converted gaseous nitrogen into a solid state by compressing it between two diamond anvils under a pressure equivalent to 1.7 million atmospheres. The resulting solid resembled ice yet possessed a diamond‑like crystal lattice. When the pressure was released at temperatures below –173.15 °C (100 K), the solid remained stable. The phase transition releases substantial energy, prompting physicist Dr. Richard M. Martin to speculate about nitrogen’s potential as a high‑energy rocket propellant.
