Nitrogen (N2)

Summary: Nitrogen (N₂) is a diatomic molecule in which the two nitrogen atoms share three pairs of electrons in a triple covalent bond, each keeping one lone pair; the very strong N≡N bond makes the gas extremely unreactive, and it forms about 78% of air. Tags: igcse chemistry Created: 2026-07-18

Nitrogen (N₂) is a diatomic Molecule of the Element nitrogen and the syllabus example of a triple covalent bond. Each nitrogen atom has five valence electrons and needs three more to complete its octet; by sharing three pairs of electrons with each other, both atoms achieve a full outer Electron Shell of 8 through Covalent Bonding rather than electron transfer (compare Ions and Ionic Bonds). Each atom also keeps one lone pair that plays no part in bonding. The N≡N triple bond is exceptionally strong and requires a very large amount of energy to break (see Bond Energy Calculations), which is why nitrogen gas is very unreactive at room temperature despite making up about 78% of clean, dry air (see Composition of Air). This inertness must be overcome industrially: in the Haber process, nitrogen is combined with hydrogen at high temperature and pressure over an iron catalyst to make Ammonia, the starting point for nitrogen fertilisers.

Bonding: Dot-and-Cross Description

In a Dot-and-Cross Diagram of N₂, one atom’s electrons are drawn as dots and the other’s as crosses:

• Each N atom contributes 3 electrons to the bond, so the region between the atoms contains 3 shared pairs (three dots and three crosses) — a triple covalent bond.
• Each N atom keeps 1 lone pair (two non-bonding electrons) drawn on its outer side.
• After sharing, each atom counts 8 outer electrons: 6 in the triple bond + 2 in its lone pair — a full octet, matching a Noble Gas Electronic Configuration.

Displayed formula: N≡N.

Key Data

Physical Properties

• A simple molecular gas with very low melting and boiling points (boils at −196 °C) — boiling overcomes only the weak Intermolecular Force between molecules; the triple bond itself is never broken by a change of state.
• Colourless, odourless and only slightly soluble in water.
• Slightly less dense than air.
• Does not conduct electricity — no mobile ions or delocalised electrons.

Why Nitrogen Is So Unreactive

Breaking the N≡N triple bond requires a very large input of energy (a very high bond energy), so nitrogen behaves almost like the Group 0 Noble Gases under ordinary conditions. Reactions involving N₂ only proceed at high temperatures (e.g. in car engines, where nitrogen and oxygen form oxides of nitrogen — see Air Pollution) or with catalysts and harsh conditions (the Haber process).

Uses

• Haber process — N₂ + 3H₂ ⇌ 2NH₃ at about 450 °C, 200 atm, with an iron catalyst, producing Ammonia for fertilisers (see Reversible Reactions).
• Inert atmosphere — unreactive nitrogen blankets food packaging and chemical processes to prevent oxidation.
• Liquid nitrogen — used as a very cold refrigerant (−196 °C) for freezing food and biological samples.
• Obtained industrially by fractional distillation of liquid air (see Composition of Air and Separation Techniques).

Sources

• Cambridge IGCSE Chemistry 0620 Syllabus (2023-2025) — Section 2.5, Cambridge Assessment International Education

Common Misconceptions