Dictionary of Chemistry [6th Ed.]

atom. Nitro compounds are made by

*nitration reactions. They can be re-

duced to aromatic amines (e.g. ni-

trobenzene can be reduced to

phenylamine). See also explosive.

nitrogen Symbol N. A colourless

gaseous element belonging to *group

15 (formerly VB) of the periodic

table; a.n. 7; r.a.m. 14.0067; d. 1.2506

gdm–3; m.p. –209.86°C; b.p. –195.8°C.

It occurs in air (about 78% by volume)

and is an essential constituent of pro-

teins and nucleic acids in living or-

ganisms (see nitrogen cycle).

Nitrogen is obtained for industrial

purposes by fractional distillation of

liquid air. Pure nitrogen can be ob-

tained in the laboratory by heating a

metal azide. There are two natural

isotopes: nitrogen–14 and nitro-

gen–15 (about 3%). The element is

used in the *Haber process for mak-

ing ammonia and is also used to pro-

vide an inert atmosphere in welding

and metallurgy. The gas is diatomic

and relatively inert – it reacts with

hydrogen at high temperatures and

with oxygen in electric discharges. It

also forms *nitrides with certain

metals. Nitrogen was discovered in

1772 by Daniel Rutherford (1749–

1819).

A

• Information from the WebElements site
  nitrogen cycle One of the major
  cycles of chemical elements in the

nitrogen 374

n

nitrogen fixation

by lightning

protein in

plants

protein in

animals

nitrites

nitrification

feeding

death death

nitrogen in

bacteria

nitrogen in

the

atmosphere

nitrates in

the soil

denitrification

nitrification

nitrogen fixationnitrogen fixationnitrogen fixation

by bacteriaby bacteriaby bacteria

oxides of

nitrogen in

the

atmosphere

nitrificationnitrificationnitrification

ammonia in

dead

organic

matter

uptake byuptake byuptake by

rootsrootsroots

Nitrogen cycle