Point 5 of 21 — Module 9 — Components and Layers of the AtmosphereQuestion bank: 1 questions (0 with pictures)
05 3.1 Nitrogen (N₂) — about 78 %
Enters the atmosphere from the decomposition of dead plants and animals and from the gases of volcanic eruptions.
It is largely inert: it does not easily react with other gases or elements, because the two atoms in the N₂ molecule are joined by a very strong triple covalent bond (N≡N, bond energy ≈ 945 kJ/mol). Reactions of nitrogen need special conditions: lightning or extremely high temperatures (such as in engines).
As a result, the proportion of nitrogen oxides in the atmosphere is very low. (This answers the question: "although nitrogen is highly abundant its oxides are found in very small quantities because there is a strong triple bond between the two nitrogen atoms, making it largely inert".) Lightning makes NO (N₂ + O₂ → 2NO), which is oxidised to NO₂ and carried down by rain as nitrate, a natural fertiliser.
Biologically, nitrogen is needed for proteins and nucleic acids, but most organisms cannot use N₂ directly; nitrogen-fixing bacteria in soil and root nodules do it.
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