Nitrogen

Nitrogen: the essentials

 Brief description: nitrogen is a Group 15 element. Nitrogen makes up about 78% of the atmosphere by volume but the atmosphere of Mars contains less than 3% nitrogen. The element seemed so inert that Lavoisier named it azote, meaning "without life". However, its compounds are vital components of foods, fertilizers, and explosives. Nitrogen gas is colourless, odourless, and generally inert. As a liquid it is also colourless and odourless.

When nitrogen is heated, it combines directly with magnesium, lithium, or calcium. When mixed with oxygen and subjected to electric sparks, it forms nitric oxide (NO) and then the dioxide (NO₂). When heated under pressure with hydrogen in the presence of a suitable catalyst , ammonia forms (Haber process). Nitrogen is "fixed" from the atmosphere by bacteria in the roots of certain plants such as clover. Hence the usefulness of clover in crop rotation.

Image adapted with permission from Prof James Marshall's (U. North Texas, USA) Walking Tour of the elements CD.

The result of touching nitrogen triiodide (NI₃)! Nitrogen triiodide is dangerously percussion sensitive (only to be demonstrated by a professionally qualified chemist following a legally satisfactory hazard asessment). Improperly done, this reaction is dangerous!

Cartoon by Nick D Kim (nearingzero.net, used by permission).

Isolation

Isolation: there is never any need to make nitrogen in the laboratory as it is readily available commercially or through in-house air liquefaction plants. However the decomposition of sodium azide is one route to N₂ and decomposition is ammonium dichromate is another. Both reactions must only be carried out under controlled conditions by a professional.

NaN₃ (300°C) → 2Na + 3N₂

(NH₄)₂Cr₂O₇ → N₂ + Cr₂O₃ + 4H₂O

Nitrogen is made on massive scale by liquefaction of air and fractional distillation of the resulting liquid air to separate out oxygen and other gases. Very high purity nitrogen is available by this route.

WebElements Shop

WebElements now has an online shop at which you can buy periodic table posters, mugs, T-shirts, games, molecular models, and more.