Nitrogen in the Air and in Compounds

Air ≈ 78% N₂ (by volume in dry air). N₂ has a triple bond N≡N → hard to break → inert as an element. Key nitrogen compounds in school chemistry: NH₃, HNO₃, nitrates (NO₃⁻). Haber process: N₂ + 3H₂ ⇌ 2NH₃ (industrial ammonia). Ammonia links to fertilisers and to nitric acid / nitrate chemistry.

Most of the nitrogen students meet is not “free” reactive N atoms but molecular nitrogen in the atmosphere. About four-fifths of dry air is N₂. That abundance matters for living systems and industry, yet N₂ itself is reluctant to react because breaking the triple bond needs a large energy input. Once nitrogen is combined, the story changes. Ammonia (NH₃) is the central industrial nitrogen compound from the Haber process. From ammonia and related pathways, chemistry leads to nitric acid (HNO₃) and to nitrate salts used as fertilisers. So “nitrogen in air” (elemental N₂) and “nitrogen in compounds” (NH₃, HNO₃, NO₃⁻) are two different chapters of the same element. Exam link: name the approximate percentage of N₂ in air, state that N≡N makes N₂ inert, and connect Haber to NH₃ — not to H₂SO₄ (that is the Contact Process).

Air is mostly nitrogen gas, N₂ — about 78%. N₂ molecules are held by a strong triple bond, so they do not react easily. Important compounds: ammonia NH₃, nitric acid HNO₃, and nitrates. Factories make ammonia from N₂ and H₂ by the Haber process.

Treat atmospheric nitrogen as N₂ with N≡N. Inertness explains why plants cannot use air nitrogen directly without fixation (biological or industrial). Haber: N₂ + 3H₂ ⇌ 2NH₃ under high pressure with a catalyst (iron-based in the school story). Ammonia is the gateway to fertilisers and to nitric acid / nitrates. Do not confuse Haber (ammonia) with Contact Process (sulphuric acid).

The triple bond and the resulting high activation energy for N₂ reactions under ordinary conditions explain both the stability of air nitrogen and the need for specialised routes (Haber; biological nitrogenase) to make usable nitrogen compounds. Track oxidation states mentally: N₂ (0) → NH₃ (−3) → HNO₃ / nitrates (+5). School answers should name percentage, bonding reason for inertness, and Haber stoichiometry without inventing Contact-Process details here.

Air ≈ 78% N₂ · N≡N → inert · NH₃ / HNO₃ / nitrates · Haber = ammonia (not H₂SO₄).