The Elements : Nitrogen


Name Symbol Atomic Number Electronic Structure Melting Point (°C) Boiling Point (°C)
 Nitrogen  N 7 2 - 5 -210.00 -195.79

Nitrogen is element No 7. The name comes from the Greek for producer of nitre. Nitre (KNO3) is a crystal used in gunpowder and fertilisers.

Compounds with NO3 in them are called Nitrates and these are very common in the Earth's crust. Nitrogen forms about 0.005% of the atoms in the crust of the Earth.

Elemental Nitrogen is a diatomic molecule, (N2) and is the most common gas in the Earth's atmosphere, making up 78% by volume. It is colourless and odourless. Nitrogen is normally unreactive in this elemental state. However during lightning flashes, the intense energy causes Nitrogen to combine with Oxygen and water to give a weak acid rain. This acid helps put nitrates back into soils so is a natural fertiliser.

Ammonia (NH3) and Nitric Acid (HNO3) are important industrial compounds. Many explosives, for example Tri-nitro Toluene (C7H5N3O6, more commonly known as TNT) and Nitroglycerine, contain Nitrogen.

Ammonium Hydroxide (NH4OH) is an alkali so nitrogen forms both acidic and alkaline compounds. Hydrazine (N2H4) is a poweful fuel used in rockets.

Nitrogen forms several oxides: Nitric Oxide (NO, a colourless, odourless insoluble gas), Nitrous Oxide (N2O a sweet smelling gas used as an anesthetic and known as "laughing gas") and Nitrogen Dioxide (NO2, a brown pungent gas).

Nitrogen is very slightly soluble in water; this solubility causes problems for deep sea divers and can lead to a fatal problem known as the bends. When a diver ascends, bubles of Nitrogen are released and gather in the joints causing intense pain and can be fatal.

Higher animals do not use Nitrogen directly. A few specialised bacteria residing in nodules of certain plant roots can utilise Nitrogen from the air. These can convert the element into organic compounds in a process called Nitrogen Fixing.

Nitrogen forms many organic compounds, the most important of which are the Amino Acids. The simplest Amino Acid is Glycine (NH2CH2CO2H). These acids contain the NH2 group which is alkaline and the CO2H group which is acidic. This dual property allows Amino Acids to join together into huge molecules called Protens which are critical for all living organisms. Although life uses about 20 or so Amino Acids, they can combine in countless ways to form all the proteins and enzymes known.

The DNA molecule that allows living organisms to reproduce contains Nitrogen. This large molecule consists of a backbone of sugars (Carbohydrates) linked together by four Bases (Adenine, Cytosine, Guanine and Thymine) and is shaped like a double helix. These Bases consists of rings of Carbon and Nitrogen atoms.

A common animal waste product, Urea (NH2CONH2) is a type of Organic compound called an Amide. The most notorious member of this family of chemicals is Thalidomide which was used a sedative in the early 1960s and produced children without limbs when taken by pregnant women.

Alkaloids also contain Nitrogen. The most famous examples are Nicotine (C8H10N4O2) and Morphene.

The simplest Organic compound containing Nitrogen is Hydrogen Cyanide (HCN), a very poisonous liquid also known as Prussic acid. This kills by interfering with enzymes that control respiration.

The human body itself is made up of about 3% of Nitrogen.

The Nitrogen atom contains 7 electrons arranged in two shells (2, 5). Although elemental Nitrogen is a mainly inert gas, its compounds play a critical role in living creatures.

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