Nitrogen (N) — Atomic Number 7

Nitrogen is a chemical element with the symbol N and atomic number 7. It is a colourless, odourless diatomic gas that makes up 78% of Earth’s atmosphere. Its strong N≡N triple bond makes it very unreactive. The name comes from Greek nitron + genes (“nitre-forming”).

At a Glance

Discovery

Discovered in 1772 by Scottish physician Daniel Rutherford, who removed oxygen and CO₂ from air and found the remaining gas extinguished flames and was “noxious.”

Chemical Properties

The N≡N triple bond (one of the strongest known) makes N₂ extremely unreactive at room temperature.

Key Reactions

1. Haber Process: ${\text{N}}_2+3{\text{H}}_2\rightleftharpoons 2{\text{NH}}_3$ (iron catalyst, 450 °C, 200 atm)
2. Ammonia with acid: ${\text{NH}}_3+\text{HCl}\to {\text{NH}}_4\text{Cl}$ (white smoke)
3. Lightning: ${\text{N}}_2+{\text{O}}_2\to 2\text{NO}$ (at very high temperatures)

The Nitrogen Cycle

1. Nitrogen fixation — N₂ → NH₃/NH₄⁺ (by bacteria or Haber Process)
2. Nitrification — NH₄⁺ → NO₂⁻ → NO₃⁻
3. Assimilation — plants absorb nitrates to make proteins
4. Denitrification — NO₃⁻ → N₂ (returned to atmosphere)

Compounds & Uses

IGCSE Essentials

1. Diatomic N₂ with triple bond — very unreactive
2. Haber Process: Fe catalyst, 450 °C, 200 atm
3. Test for ammonia: damp red litmus turns blue
4. Makes up 78% of air

Sources

• Nitrogen — Wikipedia
• Nitrogen — Ptable.com
• Nitrogen — RSC Periodic Table